Multicast Fiber Bragg Structures in Microwave Photonics Sensor Systems

Abstract

The article describes the transition concept from addressable fiber Bragg structures and microwave-photonics sensor systems based on them to multicast fiber Bragg structures. The difference between multicast structures and address structures is that in the fiber Bragg structure formes three or more super narrow-band frequency components, spaced from each other by the microwave frequency. The central frequencies shift of multicast Bragg structures is determined by the result of processing the signal of optical frequencies beats at the photodetector, which parameters judge the applied physical fields. We see the solved problem of uniquely determining the central (Bragg) frequency shift of the multicast fiber Bragg structure, with a unique set of address frequencies.

Addressed Combined Fiber-Optic Sensors as Key Element of Multi-Sensor Greenhouse Gas Monitoring Systems

“…The sensor number Wavelength (m) Reflectance will be less, if the bandwidth is decreased to 120 MHz (which is corresponded to the FBG recording technology with a minimum bandwidth of 1 pm [37]). The existing methods of the AFBS central wavelength determining, based on the optical filter with an inclined profile [22] and based on the Fast Fourier Transform [25], allow determining the absolute temperature with an error not exceeding ±0.1 °C and ±0.01 °C respectively. The main condition of the accurate temperature determination is equality of the reflection coefficients Ri of both FBGs forming ACFOS.…”

“…It consists of a broadband optical light source (e.g., a super luminescent diode), an optical filter with a predefined frequency response with an inclined profile and a photodetector. The AFBS interrogation principle allows combining several AFBS with the identical central wavelengths and the different address frequencies into a unified measurement system [22,25].…”

Influence of Two-Frequency Radiation Intensity Fluctuations on the Output Signal of a Vortex Optical Fiber Forming OAM Address in Polyharmonic Sensor Technology

“…When constructing fiber-optic and radio-photonic sensor networks (RPSNs) based on a plurality of fiber Bragg structures (FBS), there is a task of getting a unique address for every sensor element (grating). The complexity of this task is due to the high cost of interrogation devices, associated with the applied sensor multiplexing technologies, such as wavelength, time, frequency, polarization and spatial division multiplexing [15][16][17][18]. The complexity of the multiplexing technology applied and polling technologies is also explained by another important factor-the polled sensors, as a rule, are not adapted for address polling, therefore any overlap of the FBS spectra leads to significant measurement errors.…”

“…As a rule, in modern RPSNs, interrogation of spectrally-encoded FBS is performed in real-time by determining the autocorrelation function between the spectrum reflected from the sensor and its code signature [15,16]. Several works have demonstrated the detection and tracking of sensors for efficient measurement of temperature and deformation even in the case of overlapping spectra using Slepyan codes based on orthogonal discrete extended spheroidal sequences [15,16]. However, for their interrogation, a source of two-frequency scanning radiation and an electronic vector analyzer are required to carry out additional calculations and processing.…”

“…The indicated drawback was partially eliminated due to the application of the method of processing the complex signal received from the AFBS array with the same central frequency and various difference frequencies. This method made it possible to solve the problem of unambiguous determination of the positions of the central frequencies of all AFBSs in the array of sensors [15,16]. But if the RPSN size increases, the listed problems will arise again.…”