Breath is one of the most important physiological features of human life. In particular, it is significant to monitor the physical characteristics of breath, such as breath frequency and tidal volume. Breath sensors play an important role in the field of human health monitoring. However, an electronic breath sensor is not stable or even safe when the patient is in a Magnetic Resonance Imaging (MRI) system or during any oncology treatment that requires radiation and other high electric/magnetic fields. Fiber-optic-based sensors have attracted a considerable amount of attention from researchers since they are immune to electromagnetic interference. Here, we propose and demonstrate a fiber-optic-based relative-humidity (RH)-sensing strategy by depositing Ti₃C₂T_x nanosheets onto an etched single-mode fiber (ESMF). The humidity sensor function is realized by modulating the transmitted light in the ESMF using the excellent hydrophilic properties of Ti₃C₂T_x. Experiments show that the coated Ti₃C₂T_x nanosheets can effectively modulate the transmitted light in the ESMF in the relative humidity range of 30~80% RH. The sensor’s fast response time of 0.176 s and recovery time of 0.521 s allow it to be suitable for real-time human breath monitoring. The effective recognition of different breath rhythms, including fast, normal, deep, and strong breathing patterns, has been realized. This work demonstrates an all-optical Ti₃C₂T_x-based sensing platform that combines Ti₃C₂T_x with an optical fiber for humidity sensing for the first time, which has great promise for breath monitoring and presents novel options for gas-monitoring applications in the biomedical and chemical fields.

Temperature detection is of significance in environmental control, health care and biomedical engineering. However, surrounding conditions, e.g., refractive index (RI), relative humidity (RH), usually affect the performances of common temperature sensors or hinder the signal demodulations. Here, we propose a compact plasmonic fiber probe for selective temperature detection. This fiber probe is fabricated through integrating a metal-deposited nanohole array template onto a multimode fiber tip facet using optical adhesive. No extra processing is required for the fiber platform, guaranteeing the fabrication efficiency and device strength. Due to the thermal expansion and contraction, the effective RI of the adhesive varies, resulting in that the resonance wavelength of the nanohole array/adhesive interface is sensitive to external temperature change. A linear response with a high temperature sensitivity of 142.5 pm/°C is realized in the range of 20 to 60 °C. Moreover, a response time of 2.11 minutes and a recovery time of 4.09 minutes are obtained. The plasmonic fiber probe possesses an excellent selectivity, compactness, easy-fabrication, which will release its potential in versatile application scenes where a temperature selectivity is preferred. Moreover, benefiting from the tunability of nanohole array, the performance of the fiber probe can be optimized on demand, e.g., operation wavelength, bandwidth, sensitivity, etc.

Tamm plasmon polariton (TPP) is a cavity mode confined in a multilayer structure consisting of a distributed Bragg reflector and a metallic layer. It can be excited with varied polarizations and any angle of incidence, attracting significantly growing attention recently. To date, the majority of TPP structures are constructed with gold or silver. The qualification of aluminum as an alternative material for TPP mode is pending. Here, we show that it is possible to realize comparable characteristics with aluminum (Al)-based TPP structures, in terms of spectral behavior, quality factor (Q-factor), and electric field enhancement. Experimentally, we demonstrate that Al is qualified for the TPP mode with an exceptionally narrow linewidth (∼17 nm), high Q-factor (∼35.8), and moderate field enhancement (2.38-fold) in the visible band. Moreover, we found that Al-based TPP structures are more tolerant to polarization divergences (with a polarization splitting of only 11 nm at the incidence angle of 50°) compared to noble metal counterparts. This work paves the way toward the usage of Al as a viable and low-cost material for TPP devices beyond noble metals.

Accurate measuring of mechanical displacement is essential for most technologies. Here, we introduce a novel chirped fiber Bragg grating (CFBG) displacement sensor that enables ultra-sensitive measurement of a transverse displacement by mapping it into the phase-shift distribution of the CFBG. The displacement sensor is implemented by introducing a nonpermanent phase-shift on the CFBG with the assistance of MXene’s excellent photothermal effect. The phase-shift distribution can be used as a marker on the scale, and a high-resolution spectrometer observes the phase-shift markers so that a displacement sensor can be realized. The results of the proof-of-concept experiments show that the sensitivity of the sensor can reach 0.88 nm/mm with a linearity coefficient of 0.998 over a 10 mm range, and the displacement resolution of the sensor is about 12 μm. Our scheme is intrinsically stable and could be implemented as a compact sensor, using a cost-effective sensor design. This sensor can offer aerospace, biomedical, and machining applications, especially in harsh and closed environments with strong electromagnetic interference.