Fiber Bragg Gratings (FBGs) are an elegant breed of intrinsic sensors which are deployed along the length of an optical fiber. The individual FBGs is fabricated by inscribing an invisible permanent periodic refractive index change in the core of the optical fiber. When an incidence spectrum of light propagates through the grating, a specific wavelength named the "the bragg wavelength" is reflected back while the rest of the spectrum is transmitted unaffected. When an external axial strain is induced, the FBG reacts accordingly, causing a proportional shift in the reflective Bragg wavelength. With a one time instrument calibration, strain values and many other derived parameters can be measured dynamically. A key advantage of FBGs is that measurement points can be fabricated as an array of independent sensors along the same fiber, enabling multiplexed or even distributed measurements. These mulitiplexed FBG sensors can also be used to monitor different parameters such as temperature (in real time), vibration, strain, weight, and so on.

On the other hand, Photonic-crystal fiber (PCF) is a new class of optical fiber based on the properties of photonic crystals. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber (PCFs that confine light by band gap effects), holey fiber (PCFs using air holes in their cross-sections), hole-assisted fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and Bragg fiber (photonic-bandgap fiber formed by concentric rings of multilayer film). Photonic crystal fibers may be considered a subgroup of a more general class of microstructured optical fibers, where light is guided by structural modifications, and not only by refractive index differences.

In general, regular structured fibers such as photonic crystal fibers, have a cross-section (normally uniform along the fiber length) microstructured from one, two or more materials, most commonly arranged periodically over much of the cross-section, usually as a "cladding" surrounding a core (or several cores) where light is confined. For example, the fibers first demonstrated by Russell consisted of a hexagonal lattice of air holes in a silica fiber, with a solid (1996) or hollow (1998) core at the center where light is guided. Other arrangements include concentric rings of two or more materials, first proposed as "Bragg fibers" by Yeh and Yariv (1978), a variant of which was recently fabricated by Temelkuran et al. (2002) and others.

(Note: PCFs and, in particular, Bragg fibers, should not be confused with fiber Bragg gratings, which consist of a periodic refractive index or structural variation along the fiber axis, as opposed to variations in the transverse directions as in PCF. Both PCFs and fiber Bragg gratings employ Bragg diffraction phenomena, albeit in different directions).

You may refer to the following articles for more insights into the differences between PCFs and FBGs in terms of sensing capabilities:

Article Temperature and refractive index measurement using an optica...

Article Comparing FBG and PCF Force Sensors in a Laparoscopic Smart ...

Thank you for reply

So I could not use PCF for strain nor temperture sensing, could I ?

Yes; I think will be better than fiber bragg, Although PCF has an optimized characteristics, it designed for secure and accurate operations...

PCF has better performance and design flexibility as compared to FBG.

Thank you for responding

Fiber Bragg grating sensor is mainly used for sensing pressure, strain and temperature etc. FBG sensor works on the measurement of reflected bragg wavelength with respect to different temperature/strain/pressure.

On the contrary, photonic crystal fiber offers robustness in design and structural flexibilities. PCF works on TIR or PBG principle and bestows high sensing performance (sensitivity and detection limit) compared to FBG sensor.

The efficient light guiding mechanism of PCF leads to sense a wide variety of analytes, particularly the application of PCF as a biosensor has revolutionized the current research in biomedical engineering.

So, PCF can be a better option compared to FBG in sensing applications.

The PCF has a better performance than the FBG for detection.