An asymmetric Fabry-Perot modulator is disclosed having an adjustable resonant cavity length. At least one of the first and second electrodes includes a network of electrically connected particles comprising an electroactive material, and the particles of one electrode exert a repelling force on the other electrode when the first and second electrodes are combined with an uncrosslinked precursor to the solid polymer. Each element comprises a fixed magnetic portion, a tunnel barrier portion, and a free SAF structure. The power amplifier can operate in a low power and a high power mode and the adjustments can be made to the supply voltage andor the input power vary depending on whether the power amplifier is operating in the high or low power mode.