A high sensitivity refractive index sensor based on a single mode-small diameter no core fiber structure is proposed. In this structure, a small diameter no core fiber (SDNCF) used as a sensor probe, was fusion spliced to the end face of a traditional single mode fiber (SMF) and the end face of the SDNCF was coated with a thin film of gold to provide reflective light. The influence of SDNCF diameter and length on the refractive index sensitivity of the sensor has been investigated by both simulations and experiments, where results show that the diameter of SDNCF has significant influence. However, SDNCF length has limited influence on the sensitivity. Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results with a sensitivity of 349.5 nm/RIU at refractive indices ranging from 1.33 to 1.38.

Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological–electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible with wearable optical sensors. Based on the effect of a strong evanescent field, the as-fabricated SOFS is highly sensitive to strain, achieving high sensitivity with a peak gauge factor of 450. In addition, considering the large negative thermo-optic coefficient of PDMS, temperature measurements in the range of 30 to 60 °C were realized, resulting in a 0.02 dBm/°C response. In addition, wide-range detection of humidity was demonstrated by a peak sensitivity of 0.5 dB/% RH, with less than 10% variation at each humidity stage. The robust sensing performance, together with the flexibility, enables the real-time monitoring of pulse, body temperature, and respiration. This as-fabricated SOFS provides significant potential for the practical application of wearable healthcare sensors.

A high temperature-sensitive long-period fiber grating (LPFG) sensor fabricated by the local fictive temperature modification is proposed and demonstrated. High-frequency CO₂ laser pulses scan standard single-mode fiber (SMF), and the modification zones extended to the core of SMF. Experimental results demonstrate that the LPFG temperature sensors with 600 μm grating period and 32 period numbers offer the average sensitivity of 0.084 nm/C in the temperature range of room temperature (RM) to 875°C. The LPFGs fabricated here show exponential change in terms of the spectral wavelength shift versus changes in temperature. In addition, the maximum temperature sensitivity of 0.37 nm/C is achieved by employing long-period microfiber grating (LPMFG), fabricated by the microheater brushing technique and the local fictive temperature modification. LPMFG sensor exhibits better temperature characteristics due to a thinner diameter.

The impact of airborne molecular contaminants (AMCs) on the lifetime of fused silica UV optics in high power lasers (HPLs) is a critical issue. In this work, we demonstrated the on-line monitoring method of AMCs concentration based on the Sagnac microfiber structure. In the experiment, a Sagnac microfiber loop with mesoporous silica coating was fabricated by the microheater brushing technique and dip coating. The physical absorption of AMCs in the mesoporous coating results in modification of the surrounding refractive index (RI). By monitoring the spectral shift in the wavelength domain, the proposed structure can operate as an AMCs concentration sensor. The sensitivity of the AMCs sensor can achieve 0.11 nm (mg/m³). By evaluating the gas discharge characteristic of four different low volatilization greases in a coarse vacuum environment, we demonstrated the feasibility of the proposed sensors. The use of these sensors was shown to be very promising for meeting the requirements of detecting trace amounts of contaminants.

Aerosol particle contamination in high-power laser facilities has become a major cause of internal optical component damage resistance and service life reduction. In general, contaminating particles primarily originate from stray light; therefore, it is crucial to investigate the mechanism and dynamics of the dynamic contaminating particle generation to control the cleanliness level. In this study, corresponding research was conducted on experiments and theory. We investigated the particle generation and surface composition modification under the action of a laser. We employed various surface analytical methods to identify the possible variations in the aluminum alloy surface during laser irradiations. A theoretical model for particle ejection from aluminum alloy surfaces was established by taking the adhesion force and laser cleaning force (due to thermal expansion) into account. The results show that the threshold energies for contamination particle generation and damage are around 0.1 and 0.2 J/cm², respectively. Subsurface impurities are the primary source of particles, and particle adhesion density is related to surface roughness. Pollution particle generation and splashing processes include temperature increases, phase changes, impact diffusion, and adhesion. The results provide a reference for the normal operation of high-energy laser systems. The results also suggest that the laser irradiation pretreatment of aluminum alloy surfaces is essential to improve the cleanliness level.