Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-03-11
1998-07-28
Le, Que
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
359182, G01J 350
Patent
active
057865914
ABSTRACT:
The optical filter of the invention has a optical filter section for transmitting only the light having wavelength included in the transmission wavelength band prescribed by the wavelength control signal out of the input signal light and for supplying the transmission wavelength band signal light, a low frequency signal generator, an optical coupler, a photoelectric converter, a specific frequency signal component extractor, a wavelength controller, and a signal superposer. The low frequency signal generator generates a changing signal having a previously prescribed frequency. The optical coupler branches partially the transmission wavelength band signal light through the optical filter and outputs the branched signal light from one terminal. The photoelectric converter converts the branched signal light to an electric signal. The specific frequency signal component extractor extracts the signal component of the changing signal frequency, and outputs a specific frequency signal. The wavelength controller detects the phase and amplitude of the specific frequency signal and outputs a control signal so that the phase and amplitude are adjusted to prescribed values. The superposer superposes the changing signal on the control signal and outputs a wavelength control signal to the above-mentioned optical filter. According to the optical filter of the present invention, the sweeping for wavelength setting in the initial condition is unnecessary, and the optimal condition is attained in a short time. The optimal center wavelength of the transmission wavelength band is always maintained optimal without repeated sweeping for temperature change and change with time. The signal light of a prescribed wavelength channel can be extracted based on a channel selecting signal from the multiplexed signal light.
REFERENCES:
patent: 5686722 (1997-11-01), Dubois et al.
Le Que
NEC Corporation
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