Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1980-03-04
1981-12-22
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
455619, G01J 120
Patent
active
043072941
ABSTRACT:
A free space communication receiver including a lens and a photodetector spaced along the optical axis of the lens is provided with a drive for changing the distance between the lens and photodetector to thereby shift the focal point of radiation passing through the lens relative to the photodetector. A signal level detector provides an output signal level in response to the signal from the photodetector. A logic control such as a microprocessor is connected between the signal level detector and the drive for the lens. Provided that the output signal level is below a given high threshold signal level, an automatic self-focus operation takes effect, wherein as the drive moves the focal point of the lens closer to the photodetector, the resulting increase in the output signal level maintains the operation of the drive through the logic control or microprocessor until such time as the focal point coincides with the photodetector. Further movement by the drive results in defocusing and a decrease in the signal. This decrease in the signal is detected and automatically reverses the direction of the drive so that an automatic sensing of the peak signal results. This basic automatic self-focus control works in conjunction with attenuation networks to provide a very wide range automatic gain control for the entire system. Moreover, the self-focus feature compensates for changes in the lens focal length as a result of variations in ambient temperature.
REFERENCES:
patent: 4128847 (1978-12-01), Roullet et al.
patent: 4254330 (1981-03-01), Stauffer et al.
Nelms David C.
Pastoriza Ralph B.
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