This paper reports on the first application of tapered long-period gratings (TLPGs) written in photonic crystal fibres (PCFs) using a cost-effective computer-assisted precision arc-discharge apparatus for conducting direct measurements of hydrostatic pressure up to 180 bar. The developed TLPG-PCF device displays significant potential as a highly sensitive and cost-effective pressure sensor, with a pressure sensitivity of 11.2 pm bar−1. A negligible temperature sensitivity of about 0.3 pm °C−1 of the sensor output signal was observed within the temperature range from 5 °C to 65 °C.

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Long-period grating (LPG) structures including cascaded LPGs on step index fibers and photonic crystal fibers were coated with thin films of diamond-like carbon (DLC) using plasma deposition techniques. Improvements in the coating procedures increased sensitivity to external refractive index variations indicating significant improvements in sensing capability of the hybrid structures. DLC films in the range of tens of nanometers significantly increased sensitivity of all the structures tested.

This paper presents a review, based on the published literature and on the authors’ own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors.