Accurate and real-time detection of hydrogen (H₂) is essential for ensuring energy security. Fiber-optic H₂ sensors are gaining attention for their integration and remote sensing capabilities. However, they face challenges, including complex fabrication processes and limited response times. Here, we propose a fiber-optic H₂ sensing tip based on Tamm plasmon polariton (TPP) resonance, consisting of a multilayer metal/dielectric Bragg reflector deposited directly on the fiber end facet, simplifying the fabrication process. The fiber-optic TPP (FOTPP) tip exhibits both TPP and multiple Fabry-Perot (FP) resonances simultaneously, with the TPP employed for highly sensitive H₂ detection. Compared to FP resonance, TPP exhibits more than twice the sensitivity under the same structural dimension without cavity geometry deformation. The excellent performance is attributed to alterations in phase-matching conditions, driven by changes in penetration depth of TPP. Furthermore, the FP mode is utilized to achieve an efficient photothermal effect to catalyze the reaction between H₂ and the FOTPP structure. Consequently, the response and recovery speeds of the FOTPP tip under resonance-enhanced photothermal assistance are improved by 6.5 and 2.1 times, respectively. Our work offers a novel strategy for developing TPP-integrated fiber-optic tips, refines the theoretical framework of photothermal-assisted detection systems, and provides clear experimental evidence.

A high performance humidity sensor using tilted fiber Bragg grating (TFBG) and functional graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) hybrid nano-materials was proposed. The humidity-sensitive material with three-dimensional (3D) structure was synthesized by the MWCNTs and GOs. Comparing with traditional two dimensional (2D) GOs film, water molecules could be absorbed effectively due to the larger ripples and more holes in GO/MWCNTs layers. The water molecule will fill the entire space in the 3D structure instead of air, which further enhances the absorption efficiency of the hybrid nanomaterial. TFBG as a compact and robust surrounding complex dielectric constant sensing platform was utilized. The mode coupling coefficient or the amplitude of TFBG cladding mode will vary sharply with the imaginary part of permittivity of the hybrid nanomaterial, realizing the high performance RH sensing. In the experiments, we successfully demonstrated that this 3D structural nanomaterial composed by the MWCNTs and GOs has significant advantages for expanding the range of humidity detection (range from 30% to 90%) and enhancing the detection sensitivity (0.377 dB/% RH is twice more than humidity sensor with 2D GO film). The TFBG-based RH sensor also exhibits good repeatability and stability. Our proposed humidity sensor has potential application in environmental and healthy monitoring fields.

As a carbon-free energy carrier and an attractive alternative energy source, hydrogen energy has great development potential for future considerations, and it may be the ultimate answer to the global energy crisis. Due to the high combustibility of hydrogen, hydrogen sensors will be a vital component of safe use of hydrogen. Among the various sensors, the optical hydrogen sensor can meet the requirements of intrinsic safety, online detection, surrounding immunity, and lack of spark. Hence, we demonstrate a miniature optics-mechanics synergistic fiber optic hydrogen sensor by using Pd nanofilm, it has a large response range (0.5%-3.5%), high sensitivity of -0.334 nm/1% concentration and a short response time (10s)/recovery time (25s). Experimental results reveal that the proposed optics-mechanics synergistic fiber optic hydrogen sensor is reusable, durable, and low temperature sensitive. In this optics-mechanics synergistic fiber optic hydrogen sensor, nano Pd film with a large surface-to-volume ratio allows for rapid hydrogen dissociation, and Pd lattice expansion caused by Pd-hydrogen reaction is effectively transduced into optical change. This proposed sensor integrated Pd nanofilm with optical fiber by using an optics-mechanics synergistic strategy, resulting in a compact and all-optical solution for the safe measurement of hydrogen concentration, which can be used in hazardous or space-limited environments.

Because relative humidity is an important indicator to evaluate the environment quality of production and daily life, humidity sensors have been widely used in various fields. In this work, we proposed a high-sensitivity evanescent field humidity sensor based on micro-capillary and graphene oxide (GO) film. The capillary wall was coated by GO sheets for 1, 3 and 5 cycles, and the interaction between GO and the evanescent field on the capillary wall was experimentally and theoretically investigated. We tested the performance of the sensor with a relative humidity range of 30%RH-70%RH at 25°C. The experimental results show that the sensitivity of the sensor to humidity increases with the compactness of the GO coating. In addition, considering the extinction caused by the GO sheet, the transmission loss and the number of reflections in the capillary wall, the optimal length of the capillary was investigated in order to obtain a good spectral response. Since the cycle of GO coating was controllable, we found that the sensor has a tunable humidity sensitivity. This evanescent field humidity sensor can be applied in all-fiber optic networks for environmental sensing and health monitoring.