Over the past few decades, optical fibers have been widely deployed to implement various applications in high-speed long-distance telecommunication, optical imaging, ultrafast lasers, and optical sensors. Distributed optical fiber sensors characterized by spatially resolved measurements along a single continuous strand of optical fiber have undergone significant improvements in underlying technologies and application scenarios, representing the highest state of the art in optical sensing. This work is focused on a review of three types of distributed optical fiber sensors which are based on Rayleigh, Brillouin, and Raman scattering, and use various demodulation schemes, including optical time-domain reflectometry, optical frequency-domain reflectometry, and related schemes. Recent developments of various distributed optical fiber sensors to provide simultaneous measurements of multiple parameters are analyzed based on their sensing performance, revealing an inherent trade-off between performance parameters such as sensing range, spatial resolution, and sensing resolution. This review highlights the latest progress in distributed optical fiber sensors with an emphasis on energy applications such as energy infrastructure monitoring, power generation system monitoring, oil and gas pipeline monitoring, and geothermal process monitoring. This review aims to clarify challenges and limitations of distributed optical fiber sensors with the goal of providing a pathway to push the limits in distributed optical fiber sensing for practical applications.

Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions. Based on previous publications, we suggest some appropriate sensing approaches for particular applications and identify new opportunities and needs for additional research in this area moving into the future.

The photocatalytic reduction of CO₂ to value-added chemicals, such as CH₄, is a promising carbon management approach which can generate revenue from chemical sales to offset the cost of implementing CO₂ capture technologies. To make photocatalytic conversion approaches efficient, economically practical, and industrially scalable, catalysts capable of utilizing visible and near infrared (IR) photons need to be developed. Here we investigate the sensitization of TiO₂ catalysts using PbS quantum dots (QDs) which lead to the size dependent photocatalytic reduction of CO₂ at frequencies ranging from the violet to the orange-red edge of the electromagnetic spectrum (λ ∼ 420 to 610 nm). Under broad band illumination (UV- NIR), the PbS QDs enhance CO₂ photoreduction rates with TiO₂ by a factor of ∼5 in comparison to unsensitized photocatalysts. X-ray photoelectron spectroscopy (XPS) is used to investigate the deactivation mechanism of the QD sensitizers after prolonged photoexcitation. The synthesis, characterization, and catalytic testing of these PbS sensitized TiO₂ heterostructures will aid the development of more robust, visible light active photocatalysts for carbon management applications.