Multi-channel optical hybrid filter controlled by extrinsic parameters in various phases of Eu³⁺:BiPO₄

We propose a multi-channel optical hybrid filter which can regulate into a single-channel narrowband filter (SCNBF), hybrid band filter (HBF), and the dual-channel narrow band filter (DCNBF) when the input is a broad signal. The multi-channel optical hybrid filter results from the multiple evolutions of the spectral linewidth of fluorescence (FL) signal and Stokes signal generated by the spontaneous four-wave mixing. These evolutions can be controlled by changing the extrinsic parameters (i.e., gate position, gate width, laser power, and detuning) in various phases of europium-doped BPO (Eu3+:BiPO4) as the extrinsic parameters manipulate the ratio of FL and Stokes in the composite signal (FL + Stokes) and select the energy levels. The composite signal contents vary as per the linewidth through the out-of-phase and in-phase k-vectors due to destructive and constructive interferences. The maximum bandwidth contrast we attained was 91% for SCNBF, 49% and 85% for HBF, and 90% and 88% for DCNBF.