Refractive index measurement using coupled micro-resonator laser based on parity-time symmetry breaking

The aim of the present paper is to propose a new method to measure the refractive index change of environment using parity-time symmetry-based coupled micro-resonator laser. Two analog micro-resonators are optically coupled to the point that one of them experiences gain and the other one experiences the equivalent loss. This structure satisfies the parity-time symmetry condition and as a result, the Eigen-frequency of system is real. Symmetry is broken for a certain value of gain/ loss and optical modes are divided into two branches, one experiences gain and the other experiences loss. We investigate the symmetry breaking and optical amplification conditions for different optical modes. Then we consider two special optical modes and show that their Eigen-frequency depends on the refractive index of environment. We obtain the refractive index sensitivity of 172 nm RIU-1 for the refractive index change from 1 to 1.06.