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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/√Hz.

In this paper we present an overview of the current efforts towards integration of Fiber Bragg Grating (FBG) sensor interrogators. Different photonic integration platforms will be discussed, including monolithic planar lightwave circuit technology, silicon on insulator (SOI), indium phosphide (InP) and gallium arsenide (GaAs) material platforms. Also various possible techniques for wavelength metering and methods for FBG multiplexing will be 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 will be addressed as well as interrogation techniques based on tunable micro-ring resonators and Mach-Zehnder interferometers (MZI) for phase sensitive detection. The paper will also discuss the challenges and perspectives of photonic integration to address the increasing requirements of several industrial applications.

We experimentally demonstrate the feasibility of Fiber Bragg Grating sensors interrogation using integrated unbalanced Mach-Zehnder Interferometers (MZI) and phase sensitive detection in silicon-on-insulator (SOI) platform. The Phase- Generated Carrier (PGC) demodulation technique is used to detect phase changes, avoiding signal fading. Signal processing allows us to extract the wavelength shift from the signal patterns, allowing accurate dynamic FBG interrogation. High resolution and low cost chips with multiple interrogators and photodetectors on board can be realized by exploiting the advantages of large scale fabrication capabilities of well-established silicon based industrial infrastructures. Simultaneous dynamic reading of a large number of FBG sensors can lead to large volume market applications of the technology in several strategic industrial fields. The performance of the proposed integrated FBG interrogator is validated by comparing with a commercial FBG readout based on a spectrometer and used as a reference.

We describe hybrid distributed optical fiber sensor schemes for temperature, strain and vibration measurements. In particular, we first introduce the use of cyclic Simplex coding in hybrid Raman/BOTDA distributed sensors for fast long-distance strain and simultaneous temperature measurements over the same SMF, using a single narrowband source. The same advanced coding technique is also proposed to demonstrate a hybrid distributed acoustic and temperature sensor (DATS) based on Raman and coherent Rayleigh scattering processes in a standard SMF, using a single commercial off-the-shelf DFB laser and a common receiver block.

A field trial has been performed at the CERN high-energy accelerator-mixed (CHARM) field facility, newly developed for testing devices within accelerator representative radiation environments, to validate the use of Raman-based optical fiber sensors for distributed temperature measurements in highly radiative environments. Experimental results demonstrate that Raman distributed temperature sensors, operating in loop configuration on radiation-tolerant optical fibers, are able to compensate for wavelength-dependent losses and are, therefore, robust to harsh environments, in which a mixed-field radiation, including protons, neutrons, photons, and other particles, is potentially altering the fiber material properties. The temperature profile measured on commercial radiation-tolerant optical fibers shows that a temperature resolution

In this paper we perform field validation of distributed Raman temperature sensing (RDTS) for oil leakage detection in soil. The capability of the distributed Raman sensor in detecting and locating, with high accuracy and spatial resolution, drop leakages in soil is demonstrated through a water leakage simulation in a field trial. The future trends and the high potential of the Raman DTS technology for oil and gas leakage detection in long pipelines is then outlined in this paper by reporting lab experiments demonstrating accurate meter scale temperature measurement over more than 50 km of standard single mode fiber. The proposed solution, based on distributed Simplex coding techniques, can be competitive in terms of cost and performance with respect to other distributed sensing technologies.

A cyclic pulse coding technique is proposed and experimentally demonstrated for fast implementation of long-range Brillouin optical time-domain analysis (BOTDA). The proposed technique allows for accurate temperature and strain measurements with meter-scale spatial resolution over kilometers of standard single-mode fiber, with subsecond measurement times.

Hybrid sensing is becoming a key technology in application fields requiring simultaneous distributed temperature and discrete strain measurements. Two hybrid fiber optic sensing techniques effectively combining Raman and FBG-based sensing are presented in this paper.

A novel method to improve the measurement range, resolution, and multiplexing capability of time division multiplexed (TDM) fiber Bragg grating (FBM) sensors, based on advanced cyclic pulse coding, is proposed and experimentally demonstrated. The mechanism of noise reduction by quasi-periodic cyclic coding is quantitatively demonstrated, pointing out significant improvement in dynamic strain resolution with respect to single pulse TDM FBG interrogation. The use of cycling pulse coding allows for enhanced dynamic performance of real time strain measurement with respect to other coding techniques. The proposed technique can also enhance the sensing range of hybrid optical fiber sensor systems in which continuous static temperature/strain distributions and discrete dynamic strain in specific critical points are simultaneously measured over the same sensing fiber.