Compact high-speed FBG interrogator based on a high-crosstalk AWG and wavelength jump suppression algorithm

A planar lightwave circuit-based multi-channel arrayed waveguide grating (AWG) is used as a critical part of the fiber Bragg grating (FBG) interrogation unit and designed to be integrated into the fiber grating sensing system. We designed and fabricated a high-performance, 40 channels AWG in the device, enabling whole C-band wavelength demodulation while maintaining high-measurement resolution. The AWG was designed to have 100-GHz channel spacing; the channel crosstalk was measured to be −45 dB. An AWG-based FBG interrogation system was built to analyze the characteristics of our unit. The testing result shows that our system has the capability of demodulating wavelength from 1526.438 to 1563.863 nm with wavelength accuracy within ±10 pm; the wavelength resolution is measured to be 1 pm. Our testing result confirms that an AWG-based FBG interrogator is an excellent choice for FBG sensing systems.

An efficient fiber Bragg grating (FBG) sensor integration system, which utilizes a small number of standard Telecom opto-electronics components, is presented in this paper. Wavelength-swept optical pulses were generated by driving a standard telecom DFB laser diode by high amplitude (>3 A) and short duration (300 ns) current pulses. A total laser diode's wavelength sweep in excess of 10 nm was achieved, which allows for simultaneous interrogation of several FBGs within similar wavelengths. The application of short duration wavelength-swept optical pulses also allows for time division multiplexing of small FBG arrays containing FBGs with overlapping characteristic wavelengths. When a short, wavelength-swept optical pulse is launched into the fiber containing single or multiple FBGs along its length, fractions of the launched pulse are back-reflected towards the detector. Since the launched pulse wavelength changes over the time, the reflections from the FBGs occur in the time moments that depend on the FBGs' characteristic wavelengths. Measurement of the time delay among back-reflected optical pulses is then used to determine the FBGs characteristic wavelengths. The experimental system demonstrated FBG wavelength readout resolution, which exceeded 3 pm at 1 KHz sampling rate, maximum sampling rate of over 40 KHz, and capability to readout/demultiplex over 30 FBGs located down a single optical fiber.

Fiber optical sensors (FOS) have been widely used to ensure physical parameter monitoring such as strain, temperature, vibration, etc. Fiber Bragg grating (FBG) sensors are of interest mainly as they offer relatively easy integration, multiplexing capabilities, and other advantages. A topical area of investigation for FOS integration is structural health monitoring (SHM) and perimeter-security monitoring. Different objects and infrastructures have certain needs, such as long-distance (40+ km) placement and monitoring solutions, lack of active power supply availability on the site, etc. It is vital to study and develop specific FBG profiles to ensure optimal operation of FBG in security, perimeter, and SHM solutions. In this research, we have evaluated the areas and categories in which such FOS and FBGs, in particular, have been used regarding SHM and perimeter monitoring solutions. Authors have also studied, simulated, and experimentally tested various FBGs that can be implemented for the perimeter—security applications and in SHM solutions.

Dynamic strain signals are important for many structural monitoring applications, but the high-speed interrogation of strain sensors based on fibre Bragg gratings (FBGs) remains a challenge. Arrayed waveguide grating (AWG) interrogation schemes have been proposed, and by using modelling and validation experiments several design considerations are investigated and their relationship to system performance indicators determined. The Bragg grating length has an impact on the ability of the grating to ‘observe’ the transient strain field, while the spectral widths of both the FBG and AWG influence the recovered strain resolution. The system performance was examined for both high frequency noise as well as the long-term drifts over an hour, with a strain resolution of 1.4 µε observed and drift of less than 3.1 µε h−1. The noise dependence on the relative overlap of the AWG and FBG spectra was found to be significant and the inclusion of a semiconductor optical amplifier to boost light intensity at the detectors was found to significantly improve performance with an improvement in the signal-to-noise ratio up to 200%.

The objective of this research is the construction of a structural health monitoring system that uses fiber Bragg grating (FBG) to determine the health of structures. We develop fast FBG interrogator for real-time measurement of the reflected wavelength of a multipoint FBG to monitor the broadband vibration of a structure. This FBG interrogator, which combines a wavelength-swept laser and a real-time measurement system is capable of measuring wavelength within a standard deviation of 2×10 -3 nm or less. We have demonstrated that the FBG interrogator is able to measure vibration that has a resonance frequency of 440 Hz at intervals of 0.1 ms with a multipoint FBG.

The authors propose and experimentally demonstrate a calibration process unit for mitigating the effects of nonlinearity and dependence on the ambient temperature for the fibre Fabry–Perot (FFP) filter. Additionally, the performance limits of the peak detection process unit based on the maximum detection algorithm according to the noise and the characteristics of the fibre Bragg grating (FBG) and FFP filter are presented. The experimental results obtained without and with the calibration process unit exhibited an average absolute error of <93.0 and 7.34 pm, respectively. The repeatability test results for the FBG interrogator showed an absolute error <2.19 pm. To investigate the performance limits of the peak detection process unit, the Bragg wavelength with variations in the noise of both the FBG reflection spectrum and the FFP filter transmission spectrum and with different characteristics of the FBG and the FFP filter were calculated. The calculated results for the given parameters show that the error of the mean value and the standard deviation increase with decreasing signal‐to‐noise ratios of both the FBG and FFP filter. Additionally, it was confirmed that the errors increase with the increase of the full‐widths at half‐maximum of both the FFP filter and the FBG and with the decrease of the Bragg wavelength intervals.

We present a fiber Bragg grating (FBG) interrogation method using a micro-controller board and optical filter that achieves high strain sensitivity and high dynamic range. This interrogation method allows high sensitivity detection of ultrasonic waves superimposed on low-frequency (on the order of 100Hz) vibrations of arbitrary magnitude. One possible application is <i>in-situ</i> structural health monitoring of windmill blades exposed to strong winds by using FBG sensors for detection of ultrasonic waves. Interrogator operation is based on the edge filtering method using a broadband source, fiber Fabry-Perot filter and a micro-controller board which acts as a control feedback loop that locks the filter wavelength to the mid-reflection point on the FBG spectrum. Wavelength locking method allows high sensitivity for edge filtering of high-frequency waves, while the feedback signal is the measurement of low-frequency vibration with high dynamic range. The concept of the interrogator operation and different implementations are described and discussed with experimental results.

A highly integrated optical fibre sensor for simultaneous discrete dynamic strain and distributed static strain/temperature measurements is experimentally demonstrated by combining Brillouin optical time domain analysis and time-division-multiplexed fibre Bragg grating (FBG) interrogation. A highly integrated sensor system is demonstrated by using a single laser source, one shared receiver block and broadband, low reflectivity FBGs.

In this paper we investigate the impact of intra-band incoherent crosstalk due to bi-directional WDM cross-connect (OXC) based on arrayed waveguide grating (AWG), tunable Fiber Bragg gratings (FBG) and optical circulators (OC) on the bit-error-rate (BER) performance of a WDM transmission system. This paper reveals that there is a power penalty suffered by the system due to OXC. The limiting values of crosstalk factor for a BER of 10-9 are determined. It is found that the limiting value of AWG crosstalk factor is -30dB for which the penalty is approximately 8.0dB corresponding to a FBG crosstalk factor of -60dB and a OC crosstalk factor of -50dB for a WDM system with four wavelength channels operating as 10Gb/s.

Configuration of more than N DWDM channels with only one N × N cyclic-AWG-based wavelength routing device

Multifiber Bragg grating (FBG) sensor arrays are being used in the health monitoring of aerospace structures and civil engineering works, as well as the environment monitoring. However, the field interrogations of multi FBG sensors are still a big challenge due to the lack of portable, robust, high performance multi sensor interrogation devices. We have found that by thermally scanning an arrayed waveguide gratings (AWG) based demultiplexer, a device deployed in the telecommunication networks, multi FBG sensors can be precisely monitored simultaneously. The measurement resolution of this technique can be better than one picometer (equivalent to 0.1degC for temperature sensing) and the measurement time can be as short as milliseconds. Owning to the small size and ruggedness of AWG, it is potentially feasible to fabricate an all solid (no moving parts), palm size, robust and high-resolution interrogator for multi FBG sensor applications

An experimental comparison of all optical-orthogonal frequency division multiplexing (AO-OFDM) transmission is presented, using at the receiver either a fiber Bragg grating (FBG) or an arrayed waveguide gratings (AWG). System performances are analyzed, without dispersion compensation or optical time gating.

This paper introduces ensemble deep learning (EDL) models for accurate demodulation of Fiber Bragg Grating (FBG) sensor spectra, with input training data enhanced through the numerical square method (NSM) technique. The technique combines numerical squaring with an EDL to improve prediction accuracy in noisy and overlapping spectral conditions. The proposed system uses an FBG interrogator with sensors embedded in transparent liquid containers to detect liquid level changes via Bragg wavelength shifts. However, changes in the liquid level shift the float position, causing overlap or cross-talk between adjacent sensors. To address this, the NSM enhances signal clarity by boosting authentic FBG responses and minimizing noise. Single, double, and triple NSM operations are applied to the experimental data to sharpen the reflection peaks and enhance overall signal quality, ensuring the data are well-prepared for training the EDL model. The EDL model combines CNNs for spectral feature extraction and LSTMs and GRUs for sequential pattern recognition and efficient learning, effectively capturing both spectral and sequential features. The EDL model is trained on the dataset enhanced by the NSM technique and validated using unseen experimental data to evaluate its performance. The results confirm that NSM efficiently sharpens reflection peaks, improves signal clarity, and reduces noise in FBG spectra, while the EDL model effectively demodulates the overlapping spectra. Experimental results demonstrate that the integrated NSM-EDL approach outperforms traditional machine learning and standalone deep learning models in terms of prediction accuracy, minimal errors, and computational time. The proposed method is cost-effective, hardware-efficient, and ideal for real-time multiplexed FBG sensing applications, such as liquid level monitoring.

Temperature-insensitive arrayed waveguide grating demodulation technique for fiber Bragg grating sensors

An interrogation scheme based on wavelength-to-time mapping to achieve ultrafast, high-precision, and large dynamic range interrogation of fiber Bragg grating (FBG) sensors is proposed and experimentally demonstrated. The wavelength-to-time mapping, also called temporal self-imaging effect, is realized in the optical domain, using a dispersive element that has a large group velocity dispersion. For a practical dispersive element, higher order dispersions exist, which makes the wavelength-to-time mapping nonlinear. Thus, an interrogation system based on wavelength-to-time mapping without considering the high-order dispersion would reduce the interrogation accuracy. In this paper, for the first time to the best of our knowledge, a mathematical model that incorporates higher order dispersion to achieve an accurate wavelength-to-time mapping is developed, which is then verified by a numerical simulation. An FBG-based strain sensor interrogated based on the developed wavelength-to-time mapping scheme is experimentally investigated. The system has a sampling speed of 48.6 MHz, a dynamic range as large as 20 nm, and a sensing accuracy as high as 0.87 ?? for a single-shot measurement.