  Optical cavities find diverse uses in lasers, frequency combs, optomechanics,
and optical signal processors. Complete reconfigurability of the resonant
frequency as well as the loss enables development of generic field programmable
cavities for achieving the desired performance in these applications.
Conventional reconfigurable cavities are generally limited to specific material
platforms or specific optical tuning methods and require sophisticated
fabrication. Furthermore, the tuning of the loss is coupled to the
resonance-shift in the cavity. We propose and demonstrate a simple and generic
interferometer in a cavity structure that enables quasiperiodic modification of
the internal cavity loss and the cavity resonance to reconfigure the Q-factor,
transmission characteristics, and group delay of the hybrid cavity, with simple
tuning of the optical phase in the interferometer. We also demonstrate methods
to decouple the tuning of the loss from the resonance-shift, that enables
resonance-locked reconfigurability. This structure also enables resonance-shift
to both shorter and longer wavelengths using the same phase-tuning technique,
which is challenging to achieve in conventional reconfigurable cavities. These
devices can be implemented in any guided-wave platform (on-chip or fiber-optic)
with potential applications in programmable photonics and reconfigurable
optomechanics.
