Opto-acoustic chemical sensor based on forward stimulated Brillouin scattering in optical fiber

Stimulated Brillouin scattering is well-known for providing distributed measurements in the field of optical fiber sensing. For the conventional backward stimulated Brillouin scattering, the sensing capability is nevertheless limited to temperature and mechanical strain in the core of an optical fiber. Forward stimulated Brillouin scattering (FSBS), due to the participating transverse acoustic waves, can be used to directly measure the mechanical properties of the material that surrounds a standard telecom fiber. We review our work on harnessing FSBS to extract the acoustic impedances of different liquid materials. The acoustic impedance mismatch between silica optical fiber and its surroundings determines the decay rate or the corresponding resonance linewidth of the transverse acoustic modes. We address the measurement with both time and frequency domain techniques, demonstrating accuracy of measurements up to 95%. This work could be potentially extended to realize fiber based ultrasonic chemical analysis

Impact of the fiber coating on the temperature response of distributed optical fiber sensors at cryogenic ranges

The thermomechanical behavior of a standard single mode fiber with different coating materials is theoretically analyzed under different temperature conditions. Results show that the thermal expansion/shrinkage of the fiber coating introduces an extra strain on the optical fiber and can modify its thermal response. Distributed fiber sensors based on coherent Rayleigh and Brillouin scatterings are employed to characterize the impact of different coatings on the temperature sensitivity. The standard coating with dual-layer demonstrates little influence on the thermal response at room temperature due to the softness of primary coating, but it increases the temperature sensitivity by some 50 % at ~ 220 K as the primary coating becomes stiffer at low temperature. Optical fibers with aluminum (Al) and Ormocer® coatings are also experimentally tested. All the measured results agree well with the theoretical analysis

Brillouin distributed fiber sensing at ultra-high spatial resolution

Sophisticated techniques have been recently developed to achieve centimetric spatial resolution in distributed Brillouin fibre sensing, by-passing the slow response of this optoacoustic interaction by creating a localized stationary material vibration. More than 1'000'000 resolved points are demonstrated (1 cm resolution over 10 km)

Closed-loop Controlled Brillouin Optical Time-Domain Analysis

A closed-loop controlled BOTDA distributed optical fibre sensor is proposed for tracking fast temperature-strain evolution. The measurement time is reduced by two orders of magnitude with respect to classical BOTDA sensing, while keeping the same accuracy and measurement conditions

Long Weak FBG Sensor Interrogation Using Microwave Photonics Filtering Technique

“© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”A system to interrogate photonic sensors based on long weak fiber Bragg gratings (FBGs) is illustrated and experimentally demonstrated. The FBG sensor is able to detect and measure the precise location of several spot events. The principle of operation is based on a technique used to analyze microwave photonics filters. The long weak FBGs are used as quasi-distributed sensors. Several events can be detected along the FBG device with a spatial accuracy of <1 mm using a modulator and a photodetector with a modest bandwidth of <500 MHz. The simple proposed scheme is intrinsically robust against environmental changes and easy to reconfigure.This work was supported in part by the COST Action under Grant TD1001 through the OFSeSa Project, in part by the Infraestructura through the Federacion Espanola de Enfermedades Raras Project under Grant UPVOV08-3E-008 and Grant UPVOV10-3E-492, in part by the Spanish Ministerio de Ciencia e Innovacion under Project TEC2011-29120-C05-05, in part by the Valencia Government through the Ayuda Complementaria Project under Grant ACOMP/2013/146, in part by the Research Excellency Award Program GVA PROMETEO under Grant 2013/012, and in part by the Swiss Commission for Technology and Innovation under Project 13122.1.Lavinia Ricchiuti, A.; Barrera Vilar, D.; Sales Maicas, S.; Thevenaz, L.; Capmany Francoy, J. (2014). Long Weak FBG Sensor Interrogation Using Microwave Photonics Filtering Technique. IEEE Photonics Technology Letters. 26(20):2039-2042. https://doi.org/10.1109/LPT.2014.2345611S20392042262

Optimizing Image Denoising for Long-Range Brillouin Distributed Fiber Sensing

Linear and nonlinear two-dimensional image processing approaches are analyzed with the aim of removing noise from data acquired by distributed optical fiber sensors based on Brillouin optical time-domain analysis (BOTDA). The impact of the filter parameters on the denoised data is analyzed, especially for the nonlinear image denoising method called non-local means (NLM). In particular, an optimization procedure to find the optimal parameters of the NLM method for BOTDA data denoising is proposed. The described optimization procedure has enabled, to the best of our knowledge, the first experimental demonstration of a conventional BOTDA scheme (i.e. with no modifications in the layout) capable of measuring along a 100 km sensing range over a 200 km fiber-loop, using a spatial resolution of 2 m, a frequency sampling step of 1 MHz and reaching a frequency uncertainty of 0.77 MHz with 2’000 averaged time-domain traces. The experimental sensing performance here achieved has been evaluated with a figure-of-merit (FoM) of 225’000. This is the highest FoM reached without hardware sophistication in BOTDA sensing

Distributed hydrostatic pressure measurement using phase OTDR in a highly birefringent photonic crystal fiber

Although distributed fiber-optic sensing of axial strain and temperature is a well-established technique, there are almost no demonstrations of distributed hydrostatic pressure sensing. The main obstacle for such measurements is the low sensitivity to pressure of standard optical fibers. Structured fibers, such as photonic crystal fibers can be made pressure-sensitive by means of an optimized arrangement of their internal microstructure. In this paper, we demonstrate - for the first time to our knowledge - distributed birefringence and hydrostatic pressure measurements based on phase sensitive optical time-domain reflectometry (OTDR) in highly birefringent photonic crystal fibers. We study the response to hydrostatic pressure of two dedicated pressure-sensitive photonic crystal fibers in the range from ∼0.8 bar to ∼67 bar with a 5 cm spatial resolution using a phase-OTDR approach. We find differential pressure sensitivities between the slow and fast polarization axes of the studied fibers of -219 MHz/bar and -95.4 MHz/bar. These values are ∼3.8 to ∼8.8 times larger than those demonstrated previously in distributed pressure measurements with other photonic crystal fibers

All-fiber molecular frequency reference at 2 μm based on a versatile laser modulation sideband locking and a hollow-core fiber gas cell

Sensing of atmospheric trace gases is crucial for climate monitoring and to predict global climate changes. The required global coverage and spatial resolution have driven the studies of space-borne differential absorption lidar (DIAL) instruments to remotely monitor atmospheric gases from a satellite to ground. The performance of such instruments is notably determined by the frequency stability and accuracy of a low-power continuous-wave laser that seeds the pulsed laser transmitter. For a CO2 DIAL, this reference laser needs to be stabilized with an adjustable frequency-detuning from the center of the probed molecular transition and the 2.05-μm spectral range is of high interest from a spectroscopic point-of-view [1].We have developed an all-fiber modulation sideband locking set-up enabling a laser to be locked at a controlled frequency detuning from the center of the CO2 R(30) transition at 2050.97 nm, selected for DIAL applications. The offset frequency can be directly tuned over a span ranging from some hundred MHz up to at least 3 GHz, which is the typical requirement for a space-borne CO2 DIAL. The method is depicted in Fig. 1a. It consists of a distributed feedback (DFB) laser, followed by an intensity electro-optic modulator (EOM) driven by a radio-frequency signal at fEOM provided by an amplified voltage-controlled oscillator (VCO). The EOM generates a pair of sidebands shifted by ±fEOM that are coupled into a reference gas cell. The sidebands are dithered by modulating the VCO at a frequency fm 40 kHz to implement wavelength modulation spectroscopy (WMS). An error signal is produced by demodulating the reference cell transmission signal to servo-lock one of the sidebands at the center of the transition. As a result, the unmodulated laser carrier is detuned from the transition linecenter by the frequency offset fEOM, which can be easily varied, thus making the system versatile

Flexible Slow and Fast Light Using Tailored Brillouin Spectra in Optical Fibers

Stimulated Brillouin scattering makes possible the generation of synthesized gain spectra, so that innovative slow light schemes can be realized, ranging from broadband tunable delays to a zero-gain situation identical to an ideal electromagnetically-induced transparency

Nanophotonic supercontinuum based mid-infrared dual-comb spectroscopy

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical process and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for flat-envelope, ultra-broadband mid-IR comb spectra. The mid-IR dual-comb has an instantaneous bandwidth covering the functional group region from 2800-3600 1/cm, comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, spectral resolution, and speed. In addition to the traditional functional groups, their isotopologues are also resolved in the supercontinuum based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signalling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment