Numerical observations of negative group velocity in a two-port ring-resonator circuit and its potential for sensing applications

A two-port ring-resonator circuit is studied theoretically. It is shown that superluminal and negative group velocity (vg) phenomena can occur in both a passive two-port ring-resonator circuit with loss and an active one with gain. We present numerical observations of temporal behavior of a Gaussian pulse passing through circuits having such properties. We also show that when the negative vg is ‘slow’ (|vg|<<c), there is enhanced sensitivity of the phase shift to the ring effective index changes, which suggests its potential for highly sensitive optical sensing applications.