RU-2861310-C1 - METHOD FOR INTERROGATING FIBRE BRAGG GRATINGS BASED ON PHASED ARRAYED WAVEGUIDE GRATING DEMULTIPLEXER ON PHOTONIC INTEGRATED CIRCUIT USING MACHINE LEARNING ALGORITHMS

Abstract

FIELD: measuring equipment. SUBSTANCE: invention concerns a method for interrogating a fibre Bragg grating. The method comprises stages at which the fibre Bragg grating is irradiated with broadband radiation, the radiation reflected from the fibre Bragg grating is directed through an optical circulator to the input of a spectral demultiplexer based on an arrayed waveguide grating, the reflected radiation is split into several spectral channels, the optical powers in each of the channels are recorded, the signals are converted and digitised, the reflected wavelength of the fibre Bragg grating is determined based on the recorded optical powers. The determination of the reflected wavelength of the fibre Bragg grating is carried out using a machine learning algorithm trained on a calibration data set. The calibration data set is formed by mechanically stretching the fibre Bragg grating with recording of the corresponding values of optical powers at the outputs of the AWG channels and reference wavelength values. Before training the machine learning model, the initial data is pre-processed, including the generation of non-linear features and data normalisation. EFFECT: increased accuracy and expanded dynamic range of determining the Bragg wavelength of a fibre Bragg grating. 3 cl, 4 dwg, 3 tbl

Inventors

• Shipulin Arkadij Vladimirovich
• KAZAKOV IVAN ALEKSANDROVICH
• Malakhov Kirill Maksimovich
• Barma Darya Denisovna
• Treskova Angelina Andreevna
• Kovalev Egor Evgenevich
• Kulichenko Yana Vladimirovna

Dates

Publication Date

20260504

Application Date

20251121

Claims (12)

1. 1. A method for interrogating a fiber Bragg grating (FBG), comprising the steps of:
2. irradiate the FBG with broadband radiation from a superluminescent diode (SLED);
3. direct the radiation reflected from the FBG through an optical circulator to the input of a spectral demultiplexer based on an array of waveguide gratings (AWG);
4. The reflected radiation is divided into several spectral channels using an array of waveguide gratings;
5. register optical powers in each channel using photodetectors;
6. convert and digitize signals from photodetectors using a microcontroller;
7. The reflected wavelength of the FBG (λ_B) is determined based on the recorded optical powers, while:
8. The determination of the reflected wavelength of the FBG is carried out using a machine learning algorithm trained on a calibration data set obtained for a specific combination of FBG and AWG, whereby:
9. the calibration data set is formed by mechanically stretching the FBG with recording the corresponding values of optical powers P 1 , P 2 , P 3 , P 4 at the outputs of the AWG channels and the reference values of wavelengths measured using a spectrum analyzer;
10. Before training a machine learning model, the source data is pre-processed, including generating nonlinear features and data normalization.
11. 2. The method according to claim 1, characterized in that the AWG is thermally stabilized using a thermoelectric cooler (TEC) and a PID controller based on the readings of the thermistor.
12. 3. The method according to claim 1, characterized in that the trained model ensures the determination of the reflected wavelength of the FBG in an extended spectral range compared to the calibration range without additional recalibration.

Description

AREA OF TECHNOLOGY This technical solution relates to the field of fiber-optic sensors and measurement technology, in particular to methods for interrogating fiber Bragg gratings (FBGs) to determine the Bragg wavelength, which is associated with the measured physical parameter. LEVEL OF TECHNOLOGY Various methods for interrogating FBGs are known from the prior art, based on the spectral separation of radiation reflected from the grating. FBGs provide accurate measurements of strain, temperature, and vibration in critical infrastructure [1, 2]. These sensors are interrogated by devices capable of detecting subnanometer shifts in the Bragg wavelength (interrogators). There are two main interrogator architectures: (i) tunable laser-based systems, which offer high accuracy and optical power [3], but are limited by processing speed, and (ii) spectrometer-based systems, which offer high data acquisition rates, but are limited by optical power and system size [4, 5]. Phased waveguide arrays (AWGs) based on photonic integrated circuits (PICs) represent a scalable alternative for replacing bulky spectrometers and achieving high sampling rates using fast photodiodes [6–8]. However, real-world AWG channels deviate from ideal Gaussian shapes, causing asymmetries and ripples. These deviations, along with practical factors such as superluminescent diode (SLED) output fluctuations due to thermal or ambient noise [2], reduce the accuracy of common centroid or peak ratio methods [9]. Recent work has focused on optimizing AWG layout and fabrication to reduce such effects [10, 11], but these drawbacks remain a challenge for reliable signal demodulation from FBG-based sensors. To compensate for such shortcomings, previous work has used polynomial approximations [12] or auxiliary interferometric paths [13], achieving picometer-scale resolution at the cost of complexity or size. A system for interrogating VBR is known from the prior art, described in the patent application US 20220107367 A1, Xerox Corp, published 04/07/2022. This invention application discloses a monitoring system comprising: at least one device for monitoring a power transformer of a power system, including a plurality of optical sensors located on one or more optical fibers, wherein the optical sensors are configured to measure internal parameters of the power transformer, wherein each optical sensor is located inside or on the power transformer and is configured to measure an internal parameter of the transformer that is different from an internal parameter of the transformer measured by at least one other sensor of the plurality of optical sensors; at least one detector unit, which is configured to convert optical signals of the optical sensors of the corresponding device for monitoring the power transformer into electrical signals representing the measured parameters of the transformer; and at least one optical splitter located between the one or more optical fibers and the detector units, wherein the optical splitter is configured to spatially distribute the optical signals from the optical sensors in accordance with the wavelength. The disadvantage of this system is its complexity and focus on distributed monitoring objects, which may be redundant and does not provide sufficient accuracy for high-precision measurements with one or more gratings due to potential imperfections in the spectral characteristics of the components. Another disadvantage of the known solution is the need for individual calibration of each interrogator, which increases the labor intensity and duration of the production cycle, and also increases the variability of metrological characteristics in serial production. A prior art article [A. Giacobbe, L. Tozzetti, F. D. Pasquale, S. Faralli, "Fast FBG sensor interrogation method based on silicon microring resonators," IEEE SENSORS, Rotterdam, Netherlands, pp. 1-4, October 2020] describes a method for interrogating an FBG-based sensor by intensity. This method involves passing a broadband radiation source through the interrogated FBG sensor by passing it through an optical circulator and then directing the received signal to a microring resonator (MRR), used as a bandpass filter connected to two photodetectors. Using this interrogation method, the change in the resonant wavelength of one FBG sensor (caused by mechanical action on it) is monitored and translated into a change in the power at the circuit output. The disadvantage of this method is the limited dynamic range, determined by the narrow bandwidth of the resonator, as well as high sensitivity to temperature drifts of the resonator itself. The disadvantage of the above solution is the need for individual calibration of each interrogator, which entails increased labor intensity, an increase in the duration of the production cycle, and instability of metrological characteristics under serial production conditions. The closest analogue (prototype) is a method for interrogating fiber