An Amplitude Stabilization Technique for Nonlinear Optoelectronic Filtering

The nonlinear optoelectronic (NLOE) filter represents a novel class of filters whose filtering operation is based a signal reaching a specific amplitude rather than falling within a specific range of frequencies. This amplitude filtering aspect carries with it a stringent amplitude stability requirement where the input signal must be precisely maintained at a specific level for the signal to be rejected. In many real-world settings, the signal amplitudes are not precisely known or held constant over long periods of time, which greatly inhibits the application of this filter outside the laboratory. We report here a novel amplitude-stabilization scheme that locks the signal amplitude (<; 0.004 dB) to the precise level required for filter operation. Using this stabilization technique, we demonstrate a record NLOE filter suppression of 71 dB for a 3.1 GHz interferer signal relative to a second RF signal located at an 8-kHz offset. We also show the ability to maintain a >50 dB level of suppression over a period of one hour or more.