Table 1.

Comparison of FOSs.

FOS Technology	Advantages	Disadvantages	Remarks	Main Applications
Standard FBGs	Most accepted technology, allows for point measurements of strain and temperature	Temperature and strain cross sensitivity issues	Typical strain sensitivity ~1.2 pm/µε and typical temperature sensitivity ~11.6 pm/°C	Strain, temperature, vibration, cure process, localized damage, etc.
FBGs written in MOF	Can discriminate both axial and transverse strain components of composite material with insignificant temperature sensitivity	FBGs written in bow-tie fibers have temperature and strain cross sensitivity. But FBGs written in MOF have lower strain sensitivity compared to FBGs written in bow-tie fibers.	The cross-sensitivity issue can be resolved by using FBGs written in low temperature sensitive MOFs	Multi directional strain sensing, localized damage, etc.
Interferometric fiber optic sensors	Possesses higher temperature and strain sensitivities and are flexible in terms of size	Temperature and strain cross sensitivity issue, and brittle sensor	The cross-sensitivity issue can be resolved by using low temperature sensitive MOFs	Strain, temperature, vibration, cure process, localized damage, etc.
Polarimetric sensors	Sensitivity can be tuned by choosing different optical fiber types and sensor lengths	Difficult to measure strain/temperature at localized points, provide information averaged over the sensor’s length	The cross-sensitivity issue can be resolved by using low temperature sensitive HB-PM-PCF	Strain, temperature, vibration, cure process, etc.
Fiber optic micro bend sensors	Can measure continuous strain profile in a composite material using single optical fiber	Low accuracy	Output signal is strongly attenuated by any mechanical wave propagating in the composite material	Delamination and damage detection
Distributed sensors	Can measure continuous strain/temperature profile in a composite material using single optical fiber	For better resolution require the use of spectral demodulation techniques that are expensive and bulky	Appropriate sensing technology can be selected based on the application and its requirements	Strain, temperature, delamination, damage detection
Hybrid sensors	Two or more FOS operate in a combined manner to eliminate the disadvantages of individual FOSs providing accurate and independent strain/temperature information	Since two or more sensors are employed complicated interrogation methods are needed	Capable of discriminating between strain, temperature and thermal strain	Strain, thermal strain, temperature, vibration, cure process, damage point, etc.