Long-range vibration sensing is an important tool for real-time structural health monitoring. A new, to the best of our knowledge, design of a distributed fiber-optic vibration sensor is introduced and experimentally demonstrated in this study. The proposed system utilizes the transmission of light in the forward direction for sensing, and a self-interference method for laser source simplification. To extract vibration information from phase modulation of light, two Mach–Zehnder interferometers (MZIs) are employed with a 3 × 3 coupler-based differential cross multiplication algorithm for phase calculation. A folded double-ended detection configuration allows the time-of-flight difference via cross correlation (CC) to provide vibration positioning. Experimental results demonstrate a sensing range of up to ∼80 km without optical amplification, accompanied by a position accuracy of 336 m.

The growing landscape of laser applications in ∼ 2 μm spectral region leads to the development of novel transparent media that provide low attenuation solutions for high power laser applications. This includes investigating glassy media such as heavy metal oxides (e.g. tellurite and germanate), fluoride and chalcogenides as an alternative to the most efficient and widely utilized silica glass. This review article discusses the potential of a heavy metal oxide lead-germanate glass (GeO₂-PbO-Ga₂O₃-Na₂O) for ∼ 2.1 μm laser applications, with a focus on our contribution to the field. Firstly, a comparative study of commercially available silicates and fluorides with germanate glass is presented to reveal germanate to be a favorable material for 2.1 μm laser applications. Secondly, as our contribution to the field, we present the development of the first ∼ 2.1 μm small cavity single frequency laser action in a Ho³⁺ doped GPGN glass that verifies its capability for ∼ 2 μm laser applications and beyond.

Photonic Crystal Fiber (PCF) is the innovative and vital advancement in the field of optical communication. Research is being carried out in this field to study the transmission properties of PCF and how these properties can be improved to get the most optimum design. In this paper, two different categories of PCF are used (i) single solid-core PCF and (ii) multi solid-core PCF. We evaluated the confinement loss and dispersion properties for different designs of PCF to find an appropriate design for effective propagation of light in wavelength division multiplexing (WDM) systems. For WDM systems, both the confinement loss and dispersion of the fiber should be minimized for effective propagation of light. We made different designs of PCF and compared them to achieve the best possible design. The wavelength range for WDM systems is from 1300nm to 1500nm. We studied the confinement loss and dispersion for this range of wavelengths.

A multimode fiber-based sensor is proposed and demonstrated for the detection of lead traces in contaminated water. The sensing mechanism involves using a light sheet to excite a specific group of skew rays that optimizes light absorption. The sensing region features an inline microbubble structure that funnels the skew rays into a tight ring, thereby intensifying the evanescent field. The sensitivity is further refined by incorporating gold nanoparticles, which amplify the evanescent field strength through localized surface plasmon resonance. The gold nanoparticles are functionalized with oxalic acid to improve specificity for lead ion detection. Experiment results demonstrated the significantly enhanced absorption sensitivity of the proposed sensing method for large center offsets, achieving a detection limit of 0.1305 ng/mL (the World Health Organization safety limit is 10 ng/mL) for concentrations ranging from 0.1 to 10 ng/mL.