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
$\text{Cu}^{2+}$
and
$\text{Zn}^{2+}$
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
$\text{Cu}^{2+}$
and
$\text{Zn}^{2+}$
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
$4.347 \times 10^{-4}$
nm/nM and a coefficient of determination
$\mathrm{R}^{2}$
value of 0.9922. The SCFS combination, on the other hand, has attained a sensitivity of
$4.358 \times 10^{-4}$
nm/nM and a
$\mathrm{R}^{2}$
value of 0.99277. The proposed sensing configuration holds promise for multi-point sensing in bio and chemical applications, particularly in real-time scenarios.