The authors experimentally demonstrate the feasibility of interrogating Fiber Bragg Grating (FBG) sensors using an integrated unbalanced Mach-Zehnder Interferometer and active phase demodulation on silicon-on-insulator platform. The use of an external arrayed waveguide grating at the output of the circuit allows the interrogation of multiple FBGs through wavelength division multiplexing. Signal processing employing the phase-generated carrier demodulation technique is used to extract the wavelength shift from the signal patterns, allowing accurate dynamic FBG interrogation. The performance of the proposed integrated FBG interrogator is validated by comparing it with a commercial FBG readout unit based on a spectrometer and used as a reference. Experimental results demonstrate a dynamic strain resolution of 72.3 nϵ/â\u88\u9aHz

In this paper, we present an overview of the current efforts toward integration on chip of fiber Bragg grating (FBG) sensor interrogators. Different photonic-integration platforms are discussed, including monolithic planar lightwave circuit technology, silicon on insulator (SOI), indium phosphide, and gallium arsenide material platforms. Furthermore, various possible techniques for wavelength metering and methods for FBG multiplexing are discussed and compared in terms of resolution, dynamic performance, multiplexing capabilities, and reliability. The use of linear filters, array waveguide gratings (AWG) as multiple linear filters, and AWG-based centroid signal processing techniques are presented as well as interrogation techniques based on tunable microring resonators and Mach-Zehnder interferometers for phase sensitive detection. FBG sensor interrogation based on SOI platform using active and passive phase sensitive detection is also described, demonstrating specifically the potential of passive phase demodulation for high-speed dynamic strain measurements. This paper finally presents the challenges and perspectives of photonic integration to address the increasing requirements of several industrial applications.

We present a novel phase generated carrier (PGC) demodulation technique for homodyne interferometers which is robust to modulation depth variations and source intensity fluctuations. By digitally mixing the waveform with a multitone synthetic function (a linear combination of harmonics of the modulating signal), distortion can become negligible even in presence of large variations of the modulation depth. The technique only requires two mixers and can also provide the DC component of the phase in real time, without needing any previously recorded data or ellipse-fitting algorithms. We validate the technique with simulated waveforms and with experimental data from a wavelength metering experiment using an integrated unbalanced interferometer on-chip, showing that the technique corrects distortion without increasing the noise with respect to the standard PGC technique.

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