Nowadays fiber Bragg gratings (FBG) face several challenges in fiber optic sensor systems because of their complex installation and the high cost of interrogators provided by interrogation methods and FBG multiplexing. The thing is that such features as wavelength, time, frequency, polarizing, and spatial division multiplexing necessary for most applications also need complex tools, for instance, spectrum analyzers, spectrometers with tunable interferometers, Bragg gratings, etc.
It should be noted that one more challenge for FBG sensors include “the fact that these sensors are not addressable per se, and therefore, any spectrum overlapping leads to interrogation errors.” The possible way to overcome the problem is to use the addressed fiber Bragg gratings combined with the microwave photonics interrogation technique. The addressed FBG is considered to be a specific type of fiber Bragg gratings with two narrow notches in the reflection spectrum.
The operating principle is based on the light that passes through the FBG that has two narrow optical frequencies, herein, the difference between them is less than an optical frequency and installed in the microwave range. Such an addressed frequency does not depend on stress or temperature fields, it is also independent of fiber Bragg grating’s central frequency shifting.
The addressed FBG sensors act both as a two-frequency source and as a fiber optic sensor of the measurement system simultaneously. Thus, it is possible to develop a microwave-photonic fiber optic sensor system based on arrays of the addressed fiber Bragg gratings, if the set of address frequencies in the array is regarded as orthogonal. The addressed FBGs, in their turn, allow designing multi-addressed fiber Bragg grating structures.
The thing is that multi-addressed FBGs apply three (or more) frequency carriers, while their beatings on a photodetector create three (or more) address frequencies. The combination of address frequencies enables increasing the fiber optic sensor capacity of the measurement system as well as increasing the precision of central wavelength determination. Therefore, the multi-addressed FBGs are regarded as a specific type of fiber Bragg gratings with three (or more) narrow notches in the reflection spectrum.
The operating principle of the multi-addressed FBGs is based ion the light with three (or more) narrow optical frequencies, and the difference between them is less than an optical frequency and is placed in the microwave range. Additionally, the address frequencies set in FBG sensors does not depend on strain or temperature fields, central frequency shifting as well. Finally, the multi-addressed fiber Bragg gratings are both a multi-frequency source and a fiber optic sensor of the measurement system at the same time leading to the appearance of new applications.
Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at firstname.lastname@example.org