A Fabry-Perot interferometric sensor for temperature measurement was fabricated based on a silica glass solid-core photonic crystal fiber with a central air-bore. By splicing a stub of photonic crystal fiber to a standard single-mode fiber, an intrinsic Fabry-Perot cavity was formed inside the photonic crystal fiber. Sensing experiment results show that the sensor can work stably for a consecutive 24 h under temperatures up to 1100 °C, and the short-term operation temperature can reach as high as 1200 °C (<30 min). In the measurement range of 300–1200 °C, the temperature sensitivity of the peak wavelength shift can reach as high as 15.61 pm/°C, with a linearity of 99.76%. The presented interferometric sensor is compact in size and possesses advantages such as an extended working range and high sensitivity, showing promising application prospects.

A highly-sensitive vibration frequency and acceleration sensor is demonstrated, using a liquid-filled photonic crystal fiber. The designed fiber has a unique structure that a central air-bore of microscale was introduced during fiber fabrication, for the purpose of enhanced sensitivity to mechanical perturbations. The transmission properties of this novel fiber waveguide can therefore, be significantly altered when the fiber is filled with liquids, making it a sensitive carrier to vibrations. This sensor performs stably and reliably in measuring vibration frequencies of extended range from 10 Hz to 20 kHz, as well as the detection of dual-frequency signals, damped vibrations and acceleration measurements. Extremely weak vibrations, such as finger movement and human breathing can be monitored in real-time, as a crucial feature of this sensor. The vibration mechanism is further discussed in terms of enhanced sensitivity, when the fiber is filled with liquids. This sensor possesses advantageous properties such as compact structure and enhanced sensitivity, which show promising potentials in versatile vibration signal monitoring.

Photonic crystal fibers (PCFs) with various micro to nano-scale features are of intensive interest for fiber sensing. Flexible fiber structures enable the selective control of fiber properties, such as transmission modes, dispersion tailoring, trigger of multiple nonlinear effects, and so on. In this paper, three pieces of few-mode PCFs (FM-PCFs) are designed and fabricated. Guided modes in each fiber are theoretically analyzed and experimentally observed through careful excitation. Later one of the PCFs (PCF1) is used as a fiber interferometer, based on the analyses of intermodal couplings/interferences of all PCFs. The intermodal interferences between linearly polarized (LP) core modes LP01/LP11 of PCF1 are experimentally investigated, using selective mode excitation technique. The fringe contrast and intensity of the interferences can be precisely manipulated by varying the relative energies of the LP01 and LP11 modes, as the basis for the intermodal interferometer. Different from most previous studies, the interferences are mainly limited to the two core modes, which intrinsically reduces the cross-influence from temperature variations, when this fiber is used for strain sensing. Experimentally, a strain sensor using this FM-PCF based Mach-Zehnder (MZ) interferometer, is demonstrated with a restrained temperature response. This work provides significant guidance for the construction of FM-PCF based fiber sensors with simple fabrication procedure and precisely controlled interference, and most critically, with reduced cross-sensitivity between temperature and strain.

Nested anti-resonant nodeless fiber (NANF) fusion splicing with variable structural parameters is essential yet challenging for both hollow-core fiber (HCF) research and field deployment. Here, we comprehensively investigate the impact of structural parameter variations on the mode field diameter (MFD) and corresponding NANF splicing performance. Numerical simulation results indicate that the air core diameter is the dominant factor in determining the MFD of NANF, and the MFD is approximately 70% of the air core diameter. Variations of the other structure parameters hold a negligible impact on the MFD. Numerical evaluation of splicing performance reveals that, under the condition of a fixed air core diameter, splicing between NANFs with different numbers of nested tube units (e.g., 5-tube and 6-tube NANF), introduces an intrinsic coupling loss (ICL) of ∼0.045 dB, attributed to the mode field shape mismatch rather than the angular alignment, as the ICL does not vary periodically with the rotational angle. Meanwhile, variations of the other parameters contribute less than 0.01 dB ICL. Finally, we conduct an experimental evaluation of fusion splicing performance by fabricating four types of NANFs with varying nested tube units, inner tube diameters, and nested tube layers. We characterize the angle alignment sensitivity, high-order mode excitation, and back-reflection performance when various combinations of four types of NANFs are fusion-spliced. Those results of NANF fusion splicing provide valuable insights for the standardization and flexible field deployment.

On-line fabricated fiber Bragg grating (FBG) array and its sensing potentials have attracted plenty of attention in recent years. In this paper, FBG arrays are written on-line on a two-mode fiber, and this two-mode fiber Bragg grating (TM-FBG) is further experimentally investigated for temperature and curvature sensing. The responses of this sensor were characterized by 11.2 pm/°C and −0.21 dB/m⁻¹ for temperature and curvature, respectively. Based on the measurements, a dual-parameter fiber sensing system was developed, which can realize the quasi-distributed, simultaneous detection of temperature and curvature, making it suitable for structural health monitoring or perimeter security.

Brillouin fiber laser with the non-resonance pumping configuration, has compact set-up, good wavelength tunability and high-power single-frequency-emission capability, being regarded as an important technique for highly-coherent light generation. Such Brillouin fiber lasers, using single-mode fiber (SMF) as the Brillouin gain medium, generally have high lasing thresholds and mode-hopping instabilities, resulting from the relatively-low Brillouin gain coefficient of the conventional SMF. Here, we report a compact, non-resonance-pumping Brillouin photonic crystal fiber laser that can generate kHz-level-linewidth single-frequency lasing with tens-of-mW lasing threshold. Mode-hopping instability of this laser is largely suppressed thanks to the short (∼20 m) cavity length, which gives rise to a free-spectral-range (FSR) value of ∼10 MHz properly matching the tens-of-MHz Brillouin gain bandwidth. Experimental results of both self-heterodyne and frequency-noise measurements indicate a laser linewidth of ∼1.4 kHz, corresponding to high linewidth-narrowing ratio of ∼18. No lasing line of high-order Stokes was observed in experiments as the laser pump power was gradually increased to ∼200 mW, giving a nearly-linear lasing slope.