Flexibility in engineering holey structures and controlling the wave guiding properties in photonic crystal fibers (PCFs) has enabled a wide variety of PCF-based plasmonic structures and devices with attractive application potential. Metal thin films, nanowires, and nanoparticles are embedded for achieving surface plasmon resonance (SPR) or localized SPR within PCF structures. This paper begins with an outline of plasmonic sensing principles. This is followed by an overview of fabrication and experimental investigation of plasmonic PCFs. Reported plasmonic PCF designs are categorized based on their target application areas, including optical/biochemical sensors, polarization splitters, and couplers. Finally, design and fabrication considerations, as well as limitations due to the structural features of PCFs, are discussed.

We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of $-30.82\mathrm{nm}/\mathrm{RIU}$ (refractive index unit) and $47.4\mathrm{pm}/°\mathrm{C}$ by the LPG, and $171.96\mathrm{nm}/\mathrm{RIU}$ and $10.4\mathrm{pm}/°\mathrm{C}$ by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.

We report on the fabrication and characterization of a highly sensitive temperature sensor by selectively filling the nematic liquid crystal (NLC) 6CHBT into a single void within the photonic crystal fiber (PCF) structure. The temperature response of the device is experimentally characterized, showing good linearity, repeatability, and sensitivity at around -3.90 nm/°C within the temperature range from 44°C to 53°C. The mode properties of the device are theoretically investigated, confirming the mode coupling principle and the temperature sensitivity of the device.

In this paper, we report an optical fiber Sagnac interferometer (OFSI)-based temperature sensor constructed by a selectively filled polarization-maintaining photonic crystal fiber (PM-PCF). The transmission spectrum of the OFSI is in sinusoidal form and is sensitive to temperature. Simulation results predicted a higher sensitivity by selective filling than nonselective filling. In experiments, we used an extremely low-cost process to realize the selective filling. A sensitivity of 2.58 $\hbox{nm}/^{\circ}\hbox{C}$ was achieved with an 11.7-cm-long PM-PCF. The sensitivity dependence on the infiltration length ratio was also investigated.

In this paper we present an interferometer based on photonic crystal fiber (PCF) tip ended with a solid silica-sphere for refractive index sensing. The sensor is fabricated by splicing one end of the holey PCF to a single mode fiber (SMF) and applying arc at the other end to form a solid sphere. The sensor has been experimentally tested for refractive index and temperature sensing by monitoring its wavelength shift. Measurement results show that the sensor has the resolution of the order of $8.7\times {10}^{-4}$ over the refractive index range of 1.33–1.40, and temperature sensitivity of the order of $10\mathrm{pm}/°\mathrm{C}$ in the range of 20–100 °C.

Specialty fibers have enabled a wide range of sensing applications. Particularly, with the recent advancement of anti-resonant effects, specialty fibers with hollow structures offer a unique sensing platform to achieve highly accurate and ultra-compact fiber optic sensors with large measurement ranges. This review presents an overview of recent progress in anti-resonant hollow-core fibers for sensing applications. Both regular and irregular-shaped fibers and their performance in various sensing scenarios are summarized. Finally, the challenges and possible solutions are briefly presented with some perspectives toward the future development of anti-resonant hollow-core fibers for advanced sensing.