Tunable millimeter wave photonic crystal for limiting high power pulses using weakly ionized steady state plasma

We present the transmission characteristics of pulsed 44 GHz millimeter waves (MMWs) through a plasma formed within a photonic crystal. Initially, a low density plasma ( n e = 0.3 × 10 18 m − 3 ) is sustained in a crystal vacancy defect using a continuous wave (cw) MMW power of 0.06 W. This weak plasma does not much attenuate wave transmission, but it does provide seed electrons such that dense plasma forms in response to incoming MMW pulses. The dense plasma formation limits the transmission of high power pulses through the photonic crystal. A high power pulse increases the plasma electron density and shifts the resonant frequency of the crystal vacancy in accordance with the plasma permittivity. A rapid decrease in the transmitted power is observed by following the time-evolution of the plasma. A numerical electromagnetic model estimates electron density and traces the time-evolution of the plasma during MMW pulsing. The plasma-filled photonic crystal is evaluated as a power limiter. As plasma properties are readily tunable, we observe an improved operational bandwidth for incoming pulse frequencies by controlling the cw power and gas pressure of the initial weak plasma.