Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1992-11-25
1994-10-18
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
359286, G01J 132, G02F 111
Patent
active
053570979
ABSTRACT:
An apparatus for controlling an acousto-optic filter includes a high-frequency oscillator, a beam intensity detector, a first and a second oscillator, and a first and a second controller. The high-frequency oscillator drives the acousto-optic filter and the frequency of the driving signal is finely modulated by oscillation frequency f.sub.0 of the first oscillator. The detector detects an output signal beam intensity of the acousto-optic filter. An output of the detector is synchronously detected at the frequency f.sub.0 and the frequency of the driving signal is controlled by the first controller so that the resultant detected output becomes zero. Similarly, the amplitude of the driving signal is finely modulated by the oscillation frequency f.sub.1 of the second oscillator. The output of the detector is synchronously detected at the frequency f.sub.1 and the amplitude of the driving signal is controlled by the second controller so that the resultant detected output becomes zero. The frequency f.sub.0 of the first oscillator is different from that f.sub.1 of the second oscillator. Thus, the transmittivity can be maximized and stable filter operation can be realized. The apparatus may further include another variable high-frequency oscillator or a variable low-frequency oscillator which supplies to the acousto-optic filter two or more high-frequency signals for varying transmission bandwidth of the acousto-optic filter.
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Shimosaka Naoki
Shiozawa Takahiro
Allen S. B.
NEC Corporation
Nelms David C.
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