Tunable Photonic Molecules for Spectral Engineering in Dense Photonic Integration

This chapter presents some recent advances in realizing novel devices with flexible spectral response using systems of coupled microring resonators, or photonic molecules. The design flexibility of such devices offers extra degrees of freedom to perform spectral engineering using standard tuning techniques, such as microheaters and pn junctions. The successful deployment of photonic‐based solutions across different fields depends on the ability to fully control the spectral response of the building blocks of photonic circuitry. The basic functionalities required for most applications are now available in a variety of designs and platforms but the challenge remains to realize these functionalities with devices allowing for flexible and reconfigurable spectral control. A microring resonator for instance, while presenting a certain level of design freedom and spectral tunability, has its filtering and power enhancement properties dictated by its free spectral range (FSR), linewidth, and extinction ratio (ER), which are difficult to control actively.