Optical Router and 4 × 1 Multiplexer of Coexisting Crystal Field and Non‐Hermitian Autler‐Townes Splitting Controlled by Photon–Phonon Dressing in Eu3+: BiPO4

Abstract

AbstractFor the first time, the Autler Townes‐splitting dependency on parity‐time symmetry breaking is investigated. The first‐, second‐, and third‐order splitting in spectral domain outputs obtained through different phase transitions of Eu3+: BiPO4 are explored. First‐order splitting corresponds to pure crystal field splitting attributed to the shifting of energy levels and the inherent effect of the crystal field. Second/third‐order splitting results from the coexistence of crystal field and non‐Hermitian spectral Autler Townes (SAT)‐splitting caused by single‐photon dressing coupled with the interaction of phonon and double photon–phonon dressing. It is further explored the relationship between spectral and temporal‐domain splitting obtained through the different phases of Eu3+: BiPO4 by changing the laser detuning. It is authenticated that the contributions of crystal field, photon, and phonon dressing interactions can only be individually distinguished in the spectral domain. Moreover, the experiment results suggest the analogy of an optical 4 × 1 multiplexer with a channel spacing contrast of ≈91% and an optical router with a channel equalization ratio of ≈93%.