Nonlinear Optical Angle Modulation for Suppression of RF Interference

Improved RF Interference Suppression Method

“…The modeled and measured data shown in Fig. 1 confirm the attractive features of the technique described in [2]: its nearly perfect suppression at the interferer input power of approximately +13 dBm of both the interferer at frequency f 2 (red curve) and one of the problematic third-order intermodulation distortion frequencies 2f 1f 2 (gray curve) while largely preserving the signal of interest at f 1 (blue curve). Third harmonic frequencies 3f 1 and 3f 2 (gold and black curves, respectively) are not minimized at this input power, but usually these can be readily separated from the signal of interest at f 1 .…”

“…1. Output powers from an MZ modulator-based photonic link with an input signal of interest (SOI) at -19 dBm combined with an interferer (INT) at input powers varying from -20 dBm to +17 dBm, showing substantial suppression of the interferer (red curve) at the +13 dBm input power as reported in [2]. This paper describes a technique for additionally suppressing the problematic intermodulation distortion product (green curve).…”

“…In fact, as shown in Section II of this paper, this distortion product appears at the photodetector with a magnitude exactly equal to that of the signal of interest at f 1 , and is therefore exceedingly difficult to separate from that signal. A second publication using a link architecture similar to the one in [2] reported this same undesirable side-effect [3].…”

“…A recent paper in this journal [1] surveyed 46 works published since 2003 that describe photonic techniques for RF interference suppression. One such technique suppresses an RF interferer by leveraging the compression characteristic of a photonic link in which modulation of the optical phase and subsequent conversion to intensity modulation is described by cyclic Bessel functions [2]. A low-power signal of interest (SOI) at frequency f 1 plus a higher-power interferer (INT) at frequency f 2 comprised the total input signal to a quadraturebiased Mach-Zehnder (MZ) interferometric modulator supplied with light from a 1,550-nm diode laser, and the output signals from a photodetector connected to the optical output of this modulator were recorded at f 1 and f 2 , at third harmonics 3f 1 and 3f 2 , and at problematic third-order intermodulation distortion frequencies 2f 1f 2 and 2f 2f 1 .…”

“…The measured output powers at these frequencies as the input interferer power was varied from -20 dBm to +17 dBm are shown in Fig. 1 (from [2]).…”