Utilizing thermally induced selective mode shaping for a high extinction ratio in-line fiber modulator/polarizer

Light-matter interactions of guided modes strongly depend on mode shape. This Letter presents an ultrahigh extinction ratio (ER) polarizer/modulator at λ=1.55µm, enabled by selective mode reshaping for different orthogonal modes. This bi-function device benefits from a designed side-polished fiber (SPF) with a three-layer stack of graphene/VO₂/PMMA overlay. Thermally induced insulator-metal transition (IMT) in VO₂ via a graphene microheater leads to the polarization-selective mode shaping (PSMS), which is used to manipulate orthogonal modes separately. As a result, a TE modulator (TM-pass polarizer) with an ultrahigh ER=168.4dB/mm (175.1 dB/mm) and low insertion loss (IL) of IL=3.38dB/mm (0.34 dB/mm) is achieved.