Stable electromagnetic interactions with effective media of active multilayers

Gain is a blessing and a curse for photonic designs; indeed, gain-based devices may become unprecedentedly efficient but, on the other hand, the local electromagnetic fields can increase exponentially with time and lead the systems to instability. Such stability considerations are presented for a homogenized configuration incorporating tilted active multilayers by determining the poles of its transfer functions across the complex frequency plane and analytically deriving the respective constraints. The reported stable regimes will be crucial in tuning the examined module when incorporated in photonic setups for serving multiple purposes from filtering and imaging to cloaking and lasing.