Combined Two-Component Multi-Addressed Fiber Bragg Structures

Introduction. Two-component one-address fiber Bragg structures (AFBS), a type of fiber-optic sensor, offer significant advantages. They enable the multiplexing of sets and microwave photonic interrogation at unique address frequencies. This capability allows for the construction of multi-sensor, multi-parameter networks with high accuracy and low-cost measurements by substituting optoelectronic interrogators with microwave photonic ones. Despite these advantages, AFBS also have notable drawbacks, primarily the occurrence of inter-address collisions, or false addresses, when structures move relative to each other during measurements. This can lead to situations where some address components of the AFBS coincide or are multiples of frequency. To significantly mitigate the impact of inter-address collisions, both software and hardware methods can be employed. The latter includes the formation of AFBS structures with three or more spectral components, known as multi-addressed fiber Bragg structures (MAFBS). However, the manufacturing technologies for three-component MFBS are significantly more complex than for AFBS, further complicated by the need to vary the address frequencies between the three components to ensure uniqueness. The aim of this research is to develop scientifically-based principles for constructing combined two-component multi-addressed fiber Bragg structures (CMAFBS). CMAFBS must combine the simplicity of recording and controlling address frequencies characteristic of two-component AFBS with the advantages of three-component MAFBS, which are resistant to address collisions. Methods and results. Numerical modeling of AFBS employed the gear matrix method, which is well-regarded for constructing mathematical models of fiber Bragg gratings (FBG), including those with phase inhomogeneities and AFBS. Analysis of the obtained spectral characteristics revealed that the range of changes in additional address frequencies could be formed in the range of 1.2 to 7.2 GHz, which is an order of magnitude smaller than for classical two-component AFBS. It was found that the main parameter influencing the operating mode of the structure (reflection or transmission) is the value of the induced refractive index n_mod,​ as it affects the narrowband performance requirement of both the λ-FBG component and the λ/π-FBG transparency window, as well as the ability to control additional address frequencies. This influence, along with the impact of the physical length of each FBG on the characteristics of the CMAFBS, is detailed in the paper. The final section of the paper discusses the prospects for CMAFBS use and examples of their application in multi-sensor systems within the framework of the Smart Grid Plus concept for smart energy grids. Modeling has shown that CAFBS can achieve potential temperature measurement accuracy when assessing the recorded signal by wavelength to within ±0.01 °C with a sensitivity of approximately 13 pm/°C, and by amplitude to within ±0.1 °C, depending on the parameters of the ADC used. Conclusion. The paper presents new sensitive elements for constructing addressable multi-sensor networks for monitoring various physical parameters – combined two-component multi-addressed fiber Bragg structures.