Abstract
A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long-period gratings and interferometric Structures; the fourth one reports applications or these fibers for gas and liquid sensing; finally, the last section focuses oil the exploitation of nonlinear effects in photonic crystal fibers for sensing. A brief review about splicing with photonic crystal fibers is also included.

Abstract
A brief review on suspended-core fibers for sensing applications is presented. A historical overview over the previous ten years about this special designed microstructure optical fiber is described. This fiber presents attractive optical properties for chemical/biological or gas measurement, but it can be further explored for alternative sensing solutions, namely, in-fiber interferometers based on the suspended-core or suspended-multi-core fiber, for physical parameter monitoring. © The Author(s) 2012.

Abstract
A sensing head for simultaneous measurement of temperature and strain is presented and analyzed. The proposed configuration is based on the combination of two Bragg gratings, written in different fibres and with different reflectivities, to form a single signature with a reflected step spectrum profile. This characteristic minimizes the spectrum allocated to each sensor in a series multiplexing topology. By measuring the changes in the peak wavelength and spectral width of this signature, resolutions of +/- 0.65 degrees C/root Hz and +/- 2.55 mu epsilon/root Hz were achieved for temperature and strain measurements, respectively.

Abstract
Experimental results are shown demonstrating that multiple surface plasma waves can be excited in optical fibres at the 1.5 mu m optical communications region for the range of refractive indices of aqueous media using doubly deposited tapered fibre structures, well known to exhibit small or zero sensitivity to polarization. Well-defined plasmon dips were obtained with high sensitivity to the surrounding refractive index. This characteristic, together with the substantial flexibility for local and distributed measurement associated with optical fibre sensing supported by the C-Band technology, indicate that these devices can be very advantageously used for chemical, biological and environmental sensing.

Abstract
An all-optical fibre referencing scheme for intensity based sensors which uses two identical fibre Bragg gratings is described. It provides a general and simple miniature sensor design with referencing effectiveness against system power fluctuations. The concept is demonstrated for a reflective-type displacement sensing cavity, and its potential for simultaneous measurand and temperature evaluation is evaluated.

Abstract
A low coherence interferometric system with large tracking range and self-initialization to be used for remote signal processing of fiber optic accelerometers is investigated. The tracking range of the low coherence system is 1.1 mm at low frequency. Phase resolution better than 1 mrad/ square-root Hz at frequencies below 600 Hz is obtained, with a dynamic range of almost-equal-to 90 dB. Data are presented which show that if the system were used to process the output from a compliant cylinder-type accelerometer, resolutions of approximately 10(-7) g/ square-root Hz could be achieved.