Multi-Channel Simultaneous Measurement of Cu(II) and Zn(II) Metal Ions Using Multimode Interference Based Sensors Encompassed in Fiber Ring Laser

In this research, a novel fiber-optic multimode interference based multi-channel transmissive sensors integrated into a fiber laser loop (FRL) for the detection of <tex-math notation="LaTeX">Cu²⁺</tex-math> and <tex-math notation="LaTeX">Zn²⁺</tex-math> metal ions in aqueous solution is proposed and experimentally corroborated. The multi-channel configuration includes single mode- claddingless- graded index multimode- single mode (SCGS) fiber structure and single mode- claddingless- few mode- single mode fiber (SCFS) combination in parallel for tracing <tex-math notation="LaTeX">Cu²⁺</tex-math> and <tex-math notation="LaTeX">Zn²⁺</tex-math> metal ions simultaneously and implemented in FRL setup to enhance the optical sensing characteristics. The sensing probe utilises the self-imaging effect to detect and measure the concentrations of two different metal ions. The SCGS structure has achieved a sensitivity of <tex-math notation="LaTeX">4.347 × 10⁻⁴</tex-math> nm/nM and a coefficient of determination <tex-math notation="LaTeX">R²</tex-math> value of 0.9922. The SCFS combination, on the other hand, has attained a sensitivity of <tex-math notation="LaTeX">4.358 × 10⁻⁴</tex-math> nm/nM and a <tex-math notation="LaTeX">R²</tex-math> value of 0.99277. The proposed sensing configuration holds promise for multi-point sensing in bio and chemical applications, particularly in real-time scenarios.