Self-Referenced Fiber Optic System For Remote Methane Detection

A fiber optic multisensor methane detection system matched to topology and environment of a coal mine is reported. The system involves time domain multiplexed (TDM) methane sensors based on selective absorption of source radiation by atomic or molecular species in the gas sensing heads. A two-wavelength ratiometric approach allows simple self referencing, cancels out errors arising from other contaminants, and improves the measurement contrast. The laboratory system consists of a high radiance LED source, multimode fiber, optical sensing head, optical bandpass filters, and involves synchronous detection with low noise photodiodes and a lock-in amplifier. Detection sensitivity upon spectral resolution of the optical filters has also been investigated and described. The system performance was evaluated and the results are presented.

Water quality testing is of great significance for daily water use or water use in high precision manufacturing. The use of single-photon detection technology to detect water particles is one of the important methods of physical water quality detection. However, the current water quality particle detection technology needs to be improved in the range and accuracy of turbidity detection. The paper aims to use single-photon detection technology to design a fiber optic turbidity detection system to solve the current problems of small turbidity detection range and low accuracy in a large range. In response to this, this paper has made an in-depth understanding of single-photon detection technology and designed two sets of detection schemes using the performance of photons. The first set is the transmission optical fiber turbidity detection, which can effectively detect the ultralow turbidity range and a wide range of water quality particles. The second set is a scattering optical fiber turbidity detection system, which can effectively detect water particles in the low and medium turbidity range. In this paper, the two systems were integrated into a whole system, so the results of the two detection methods can also be compared, and the detected turbidity can be obtained more accurately. The experimental results showed that for the transmission optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 11 wm, and the fitting value was 0.99; for the scattering optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 4 wm, and the fitting value was 0.99.

This paper describes the successful test of a multi-point fiber optic oxygen sensor system during the static firing of an Evolved Expandable Launch Vehicle (EELV)/Delta IV common booster core (CBC) rocket engine at NASA's Stennis Flight Center. The system consisted of microsensors (optrodes) using an oxygen gas sensitive indicator incorporated onto an optically transparent porous substrate. The modular optoelectronics and multiplexing network system was designed and assembled utilizing a multi-channel opto-electronic sensor readout unit that monitored the oxygen and temperature response of the individual optrodes in real-time and communicated this information via a serial communication port to a remote laptop computer. The sensor packaging for oxygen consisted of two optrodes - one doped with an indicator sensitive to oxygen, and the other doped with an indicator sensitive to temperature. The multichannel oxygen sensor system is fully reversible. It has demonstrated a dynamic response to oxygen gas in the range of 0% to 100% with 0.1% resolution and a response time of ≤10 seconds. The sensor package was attached to a custom fiber optic ribbon cable, which was then connected to a fiber optic trunk communications cable (standard telecommunications-grade fiber) that connected to the optoelectronics module. Each board in the expandable module included light sources, photo-detectors, and associated electronics required for detecting oxygen and temperature. The paper illustrates the sensor design and performance data under field deployment conditions.

This paper describes the successful development and test of a multipoint fiber optic hydrogen microsensors system during the static firing of an Evolved Expandable Launch Vehicle (EELV)/Delta's common booster core (CBC) rocket engine at NASA's Stennis Space Center. The hydrogen sensitive chemistry is fully reversible and has demonstrated a response to hydrogen gas in the range of 0% to 10% with a resolution of 0.1% and a response time of ≤5 seconds measured at a gas flow rate of 1 cc/min. The system consisted of a reversible chemical interaction causing a change in reflective of a thin film of coated Palladium. The sensor using a passive element consisting of chemically reactive microcoatings deposited on the surface of a glass microlens, which is then bonded to an optical fiber. The system uses a multiplexing technique with a fiber optic driver-receiver consisting of a modulated LED source that is launched into the sensor, and photodiode detector that synchronously measures the reflected signal. The system incorporates a microprocessor to perform the data analysis and storage, as well as trending and set alarm function. The paper illustrates the sensor design and performance data under field deployment conditions.

Optical fibre damage detection for an aircraft composite leading edge

A fibre optic multi-component seismic acquisition system for permanent installation on the sea floor has been developed and tested. Permanent seafloor seismic installations are an alternative to other marine seismic acquisition methods for time-lapse (or 4D) seismic reservoir monitoring. 4D seismic can assist reservoir engineers to monitor fluid injection and drainage of the reservoir, and help determine detailed reservoir fluid-flow models. The new fibre optic system uses a Dense Wavelength Division Multiplexing telemetry scheme to optically power the seismic sensors. This methodology allows for channel counts in excess of 2000 per cable. Furthermore, the fibre optic system has a very broad processing bandwidth that yields exceptional dynamic range (> 140dB), which together with low channel crosstalk and distortion, will produce high quality seismic images. The multi-component sensors at each receiver station are optical transducers made using Michelson interferometers. Avoiding in-sea electronics creates a safe and robust system, and utilisation of standard telecommunication components ensures an economically viable reservoir monitoring tool. Field trials conducted in hydrocarbon provinces demonstrate the reliability and excellent response of the fibre optic system to the seismic source. The seismic data acquired by the new fibre optic acquisition system show good correlation with data acquired in parallel using a conventional electrical seafloor acquisition system.

Based on DFBLD (Distributed Feedback Laser Diode) and harmonic detection technique, a novel fiber-optic methane detection system is constructed. The system can be applied to broad-range concentration detection of methane. Based on the approximation express of the law of Beer-Lambert, detection of methane with various concentration from 0% to 20% is completed using subtraction of background and ratio processing method, as the atmosphere surroundings are treated as background noise. The direct absorption spectra for various concentration is measured using GRIN gas cell, combined with DFBLD. The R5 line of the 2v3 band of methane is selected as the absorption peak. The system is tested online during gas mixing process and the linear relationship between system indication and concentration variation is validated. Also the stability and dynamic response characteristics are confirmed by the experiments. The sensitivity of the system can be adjusted according to the concentration level of various field environments by changing the prism distance using step motor. In the range of 0% to 20% the sensitivity of methane detection can arrive at 0.001%. So the system can be applied to various application fields and adopted as monitoring instruments for coalmine tunnel and natural pipeline.

: A capillary waveguide fiber optic probe system has been constructed which is capable of rapidly collecting Raman spectra of organic compounds in water. It consists of a dual fiber optic probe coupled to a capillary waveguide designed to increase the volume of sample interrogated by the excitation light. A Nd:YAG laser operating at 532 nm is used to generate Raman scatter at the sample in the capillary which is transmitted by the collection fiber to a notch filter holder and linear array detector. The feasibility of using this system for methane hydrate detection is evaluated through the use of organic surrogate molecules, due to the low solubility of methane in water at atmospheric pressures. The eventual application is the oceanic detection of methane gas, liquid, and solid hydrate at great depths (1000's of meters). Under these conditions, the solubility of methane increases significantly and solid hydrate may be present. The relative Raman cross sections of methane and other organic compounds relative to nitrogen are documented. The benefit of using a capillary waveguide with the dual fiber optic probe is quantitatively shown. The LOD of acetone (as a surrogate for methane) is determined and the LOD of methane under several experimental conditions is calculated. The ability to detect all three states (gas, liquid, and solid) is of great importance to the detection and characterization of ocean floor methane.

This paper explains the design of a real time fiber optic intrusion sensing system. The said system operates passively on the field, unlike most of its counterparts, without any performance compromise. Optical signal processing and electronics is discussed. Simulation results are included in order to support the design. Signal estimation is accomplished through novel stochastic estimation technique. The POD of the system is found to be greater than 90% through extensive testing.

Lightweight fiber optic intrusion detection system

A perimeter intrusion detection system (PIDS) is critical for the security of a shale gas field. Among many technologies, the fiber optic sensor-based method is the most widely used, due to its passive, low-cost, long-life, and strong anti-interference ability and strong environmental adaptability. This article proposes an event detection and classification method for a fiber optic PIDS. In general, three types of features are extracted for an improved double-threshold method to improve the probability of detection. Also, the detected intrusion events are distinguished by a support vector machine with wavelet features to reduce the nuisance alarm rate. Experiments on the PIDS in Chongqing Fuling's shale gas field show that detection algorithms based on the feature of short-time energy and short-time wavelet coefficient energy are much better, and the performance of event classification is satisfactory.

Optical wireless technology has been considered as a promising candidate to provide high-speed wireless connectivity in personal work/living spaces. Previously we proposed and demonstrated a high-speed indoor communication system by incorporating limited mobility with localization function. Furthermore, we showed that by using a novel single channel imaging receiver, better system performance can be achieved and the demonstration was based on single-mode fiber due to its low transmission loss feature. However, in most already installed inbuilding optical fiber distribution networks, multi-mode fiber was deployed since it is low-cost and easy to handle. In this paper, we experimentally demonstrate the feasibility of the proposed optical wireless personal area communication system with single channel imaging receiver based on multi-mode fiber. In addition, the wavelength-division-multiplexing (WDM) technology is also incorporated to realize an ultra-broadband connectivity in wireless personal area networks. The results show that a simultaneous operation of a 4 × 10 Gbps down-link and a 400 Mbps up-link can be realized simultaneously and the beam footprint is larger than 1 m even when a channel selecting optical bandpass filter with ~77% transmission efficiency was used.

Comparing with the conventional double-sideband (DSB) modulation in communication system, single-sideband (SSB) modulation only demands half bandwidth of DSB in transmission. Two common ways are employed to implement SSB modulation by using optical filter (OF) or electrical 90° phase shift, respectively. However, the bandwidth of above methods is limited by characteristics of current OF and electrical phase shift. To overcome this problem, an ultra-wideband microwave photonic link based on SSB modulation is proposed and demonstrated. The radio frequency (RF) signal modulates a single-drive dual-parallel Mach-Zehnder modulator, and the SSB modulation is realized by combining an electrical 90° hybrid coupler and an optical bandpass filter. The experimental results indicate that the system can achieve SSB modulation for RF signal from 2 to 40 GHz. The proposed microwave photonic link provides an ultra-wideband approach based on SSB modulation for radio-over-fiber system.

A polarisation-division-multiplexing (PDM)-based four-level pulse amplitude modulation (PAM4) fibre-free-space optical (FSO) convergent system with optical band-pass filters (OBPFs) for polarisation de-multiplexing is feasibly demonstrated for the first time. In a PDM scenario with PAM4 modulation, the transmission capacity of fibre-FSO convergent systems is enhanced four times with an aggregate channel capacity of 128 Gb/s (64 Gb/s PAM4/polarisation × 2 polarisations). With an OBPF, polarisation-tracking free de-multiplexing is attained by eliminating other optical carrier with orthogonal polarisation. An OBPF is a simple polarisation de-multiplexing scheme in which the polarisation-orthogonal carrier can be effectively de-multiplexed and the cross-polarisation interference can be nearly eliminated. Compared with traditional PDM-based fibre-FSO convergent systems with sophisticated polarisation-tracking mechanism and elaborate digital signal processing (DSP) approach, it reveals a noteworthy one with the advantage of simplicity. Through 25 km single-mode fibre transport and 500 m FSO link, sufficiently low bit error rate and qualified PAM4 eye diagrams are attained. This proposed polarisation-tracking free PDM-based fibre-FSO convergent system is notable because it not only incorporates the fibre backbone and optical wireless feeder, but it also simplifies the framework since complicated polarisation-tracking mechanism and DSP approach are not involved.

Волоконно-оптичні системи є одним з найбільш перспективних напрямків при розробці фізичної основи інформаційного простору. При реалізації оптоволоконних ліній зв'язку часто виникає необхідність узгодження оптоелектронних компонентів з різними поперечними перетинами випромінюючих і приймаючих областей і різними числовими апертурами. Варіантом такого завдання може бути з'єднання одномодового і багатомодового волокон або випромінювачів і фотоприймачів з волокнами різних типів. Одним з методів такого узгодження є створення каскадних волокон, в яких лінзове волокно і кілька ділянок градієнтних волокон інтегровано в одномодове волокно. Предметом дослідження є технології елементів волоконно-оптичних систем передачі. Метою даної роботи є створення компонентів волоконно-оптичних ліній зв’язку, що дозволяють підвищувати ефективність вводу випромінювання від джерела в оптичних світловод, зокрема одномодовий. Для досягнення поставленої мети необхідно вирішення наступних завдань: розглянути фактори, що впливають на втрати енергії при генерації і вводу випромінювання джерела в оптичне волокно, а також розробити і впровадити систему узгоджуючих елементів і дати послідовність дій для ефективного вводу випромінювання джерела в одномодове волокно. Висновки. Запропонована технічна і технологічна реалізація процесу робить можливим вводити більшу потужність в оптоелектронні лінії передачі інформації, що підвищує ефективність вводу випромінювання до 20 дБ. Визначення точності розташування сполучної площини в пристроях узгодження та взаємного розміщення випромінювачів та оптичного волокна дає можливість знизити втрати в з'єднанні до 0,1 дБ, передавати інформацію з більшою надійністю на більші відстані без регенерації і зберегти працездатність волоконно-оптичної системи в умовах впливу механічних, кліматичних і радіаційних факторів