Optical techniques for water monitoring

Clinical Imaging with Optical Coherence Tomography

The chemistry of sol-gel derived silica and refractive metal oxide has been systematically studied. Sol-gel processes have been developed for preparing porous silica and semiconductor metal oxide materials. Micelle/reversed micelle techniques have been developed for preparing nanometer sized semiconductor metal oxides and noble metal particles. Techniques for doping metal ions, metal oxides and nanosized metal particles into porous sol-gel material have also been developed. Optical properties of sol-gel derived materials in ambient and high temperature gases have been studied by using fiber optic spectroscopic techniques, such as fiber optic ultraviolet/visible absorption spectrometry, fiber optic near infrared absorption spectrometry and fiber optic fluorescence spectrometry. Fiber optic spectrometric techniques have been developed for investigating the optical properties of these sol-gel derived materials prepared as porous optical fibers or as coatings on the surface of silica optical fibers. Optical and electron microscopic techniques have been used to observe the microstructure, such as pore size, pore shape, sensing agent distribution, of sol-gel derived material, as well as the size and morphology of nanometer metal particle doped in sol-gel derived porous silica, the nature of coating of sol-gel derived materials on silica optical fiber surface. In addition, the chemical reactions of metal ion, nanostructured semiconductor metal oxides and nanometer sized metal particles with gas components at room temperature and high temperatures have also been investigated with fiber optic spectrometric methods. Three classes of fiber optic sensors have been developed based on the thorough investigation of sol-gel chemistry and sol-gel derived materials. The first group of fiber optic sensors uses porous silica optical fibers doped with metal ions or metal oxide as transducers for sensing trace NH{sub 3} and H{sub 2}S in high temperature gas samples. The second group of fiber optic sensors uses sol-gel derived porous silica materials doped with nanometer particles of noble metals in the form of fiber or coating for sensing trace H{sub 2}, NH{sub 3} and HCl in gas samples at for applications ambient temperature. The third classes of fiber optic sensors use sol-gel derived semiconductor metal oxide coating on the surface of silica optical fiber as transducers for selectively sensing H{sub 2}, CH{sub 4} and CO at high temperature. In addition, optical fiber temperature sensors use the fluorescence signal of rare-earth metal ions doped porous silica optical fiber or the optical absorption signal of thermochromic metal oxide materials coated on the surface of silica optical fibers have also been developed for monitoring gas temperature of corrosive gas. Based on the results obtained from this project, the principle of fiber optic sensor techniques for monitoring matrix gas components as well as trace components of coal gasification derived syngas has been established. Prototype sensors for sensing trace ammonia and hydrogen sulfide in gasification derived syngas have been built up in our laboratory and have been tested using gas samples with matrix gas composition similar to that of gasification derived fuel gas. Test results illustrated the feasibility of these sensors for applications in IGCC processes.

Brain oxygenation: monitoring techniques and insights into brain function and survival

Optical fiber is a powerful element in optical communication and other optical techniques. A novel optical metrology based on optical fiber techniques is presented in this paper. The advantages of this technique provide not only the mini-type apparatus but also a simple phase-shifting method to increase the measuring accuracy. A high birefringence fiber with a beat length of 1.2 mm for phase-shifting technique is introduced. The experimental set-up and the technique principle, details will be discussed. Several application examples of optical metrology based on the optical fiber set-up are presented. The application areas include displacement measurement, 3D shape measurement and nondestructive testing. One of the important features of this advanced apparatus is its ability to apply in small object measurements for the electronic industry.

Even in this digital age, SAW and Optical devices remain indispensable analogue signal processing technologies whose operation and success derive from common wave propagation phenomena. In this review I hope to explain why this is so, and will remain so for the foreseeable future. Historically, the development and exploitation of these technologies arose during the Cold War primarily from the military need for an unsurpassed signal processing capability, although both are now widely exploited in civil applications as well. Following the Introduction, this paper briefly reviews the construction, operation, attractions, and selected applications of the SAW devices developed since the invention of the Interdigital Transducer (IDT) in 1965. These devices include delay lines, bandpass filters, and the first SAW device used in anger, the dispersive delay line which was vital to the realisation of pulse compression radar. I shall also review the attractions of SAW oscillators, which I believe still enjoy an opportunity to contribute to the insatiable military need for improved overall stability. Following this I introduce some components and techniques devised by the optics community for signal and image processing since the invention of the laser in 1960, beginning with techniques for pattern recognition and the ingenious technique devised to realise real-time Synthetic Aperture Radar, (SAR) image formation. More recently, the invention and development of laser diodes and fibre optics by the telecommunications industry has led to the realisation of optical signal processing techniques whose functionality is in many respects complementary to that of SAW devices. In particular, optical techniques are now useful for the generation, delay, sampling, and distribution of signals at higher rf frequencies (and bandwidths) than SAW devices, ie at microwave and mm- wave frequencies and above, leading to the modern field of activity known as Microwave Photonics. Some current research topics in this field are described, including stable microwave generation, phased array antenna beamforming, and A/D conversion, each being relevant to future military and civil systems.

Biomedical optics has emerged as a dynamic field encompassing a range of optical devices and technologies, including light sources, lasers, sensors, optical fibers, and optical processing principles. Its impact on medical engineering and clinical applications has been profound, leading to advancements in laboratory practices, optical fibers, biosensing, imaging, radiation grading, absorption spectroscopy, and polarization sensing. This article examines the historical progression of biomedical optics, highlighting its contributions to medical imaging and diagnosis. It focuses particularly on computed tomography, fluorescence imaging, optical molecular imaging, spectroscopy, near-infrared tomography, and optical coherence techniques. Biomedical optics' development has transformed medical science by enabling non-invasive diagnosis, improving treatment planning, and enabling specific therapy. The positive outcomes of these advancements underscore the significance of biomedical optics in promoting progress in the field of medicine. The paper discusses optical technologies and their clinical implications, including spectroscopy, near-infrared tomography, optical coherence tomography, computed tomography, fluorescence imaging, and molecular imaging.

In high-speed grinding research, it is required to measure temperature within the workpiece. Present techniques are thermocouple based, and often suffer from excessive electrical noise on the signal. This thesis presents a number of novel and existing optical sensing devices that overcome this limitation and also, in some cases, offer greater performance. The optical sensors are fibre Bragg grating based and the optical techniques used to interrogate that sensor include DWDM, WDM, athermic grating, tuneable grating and coupler. Optical fibre devices are simpler to place in situ prior to the machining tests and they offer faster response and greater sensitivity than was previously possible. Results are presented from machining tests and the new devices are compared with each other and thermocouple based techniques. A method to relate internal measured temperature to machined surface temperature is also demonstrated in the context of high-speed machining.

Generation of optical pulses at repetition rates in 10s-100s GHz range beyond the limits of conventional electronics can be achieved using all optical passive techniques. Here, we report a 60 GHz soliton pulse source utilizing all optical fibre technology. The principle of operation is based on the use of dual frequency beating as a source of periodic optical signal and the transformation of the beat half-periods into optical pulses using nonlinear propagation in a novel optical fibre design which we call a Comblike Dispersion Profiled Fibre (CDPF). This fibre consists of many alternating segments of two fibre types with high anomalous dispersion and minimum absolute dispersion at the operational wavelength. In fact, the dispersion-length profile of this fibre has a comb-like shape. Previously, transformation of the optical beat signal into pulse train was demonstrated in a Dispersion Decreasing Fibre (DDF) [1]. However, the implementation of CDPF has a number of advantages: CDPF can provide significant suppression of Stimulated Brillouin Scattering (SBS) enabling the use of a narrow linewidth, low phase noise beat signal; it can provide pulse train generation over a much wider range of repetition rates and a reduction of the necessary input power; and a CDPF can be accurately produced with in advance determined properties using conventional standard types of optical fibres - Standard Telecommunication (STF) and Dispersion Shifted Fibres (DSF) and thus does not require any special technology.

In recent years many exciting developments have taken place in the area of smart structures which are designed to react to their environment by the use of integrated sensors and actuators. At the same time, important advances in lasers, fiber optics, semiconductor optoelectronics, optical and thermal imaging, and optical processing have made possible the application of optical methods in many novel ways. Optical techniques and technologies have thus a major role to play in the development of smart sensors and structures. The purpose of this paper is to present a review of some recent developments in this direction.

Fiber optic technology for real-time monitoring of down-hole well conditions is advancing rapidly in the oilfield. Discrete fiber optic sensors or fiber optic for distributed temperature measurements are relatively easy to deploy in conjunction with the production tubing string. Incorporating fiber optics into a gravel pack assembly is considerably more complex and requires several specialized equipment components. A method to mount the fiber optic conduit to the screen and protect the conduit during screen deployment, gravel packing and production is required. A sand control packer with feed- throughs for the conduit and compatible with crossover tool gravel placement methods is also required. Finally, a method to reconnect the production tubing to the gravel pack packer and establish a continuous fiber optic conduit from the surface to the end of the screen is needed. This paper describes the development and application of a gravel packing system that incorporates a conduit for fiber optics. The primary components of the system and lessons learned from a full- scale stack-up test are discussed. Technology gaps relating to fiber optic deployment tools and techniques are outlined.

In complex supply chains, the benefits and costs of technological innovations do not always accrue equitably to all parties; thus, their adoption may critically depend on sourcing relationships and incentives. In a setting with uncertain and endogenous process yield, we study the potential of two features—contract design and sourcing channel—to create mutual benefit in decentralized value chains, where suppliers bear the costs of new technologies while benefits accrue primarily to buyers. Our focus is on agricultural value chains, where parties may transact through a channel that blends farmers’ produce (“commodity-based channel”) or that allows a one-on-one interaction between farmer and processor (“direct-sourcing channel”). Our study provides insights to companies seeking to incorporate responsible sourcing strategies while also creating economic value—a concept called “creating shared value.” We identify that the technology’s “cost elasticity” drives whether switching sourcing channel, changing contract structure, or adopting an integrated change is necessary to create shared value. This highlights that value chain innovations need to be properly designed—and sometimes combined—to achieve sustainable implementation. We also find that certain simple contracts with a linear or bonus structure are optimal, while other intuitive contracts could be detrimental. Using a data set of farms in Patagonia, Argentina, we estimate that the proposed mechanism could increase average supply chain profit by 6.9% while realizing positive environmental benefits.The online appendix is available at https://doi.org/10.1287/msom.2017.0627 .This paper has been accepted for the Manufacturing & Service Operations Management Special Issue on Value Chain Innovations in Developing Economies.

The safety of SCUBA divers remains at high risk in deep-sea owing to multiple factors such as dangerous surrounding, rely upon technical equipment necessary for life support, decreased underwater navigation, and communication infrastructure. Gradual decrease and increase in water temperature and pressure corresponding to depth are among the most common problems that cause most of the fatalities in deep-sea diving. Therefore, different gadgets for accurate measurement of vital parameters, reliable navigation, and seamless communication are of prime importance. In this paper, we propose an all-optical technique for local and remote monitoring of underwater temperature and pressure for deep-sea SCUBA divers based on fiber Bragg grating (FBG) sensors and underwater optical communication-single mode fiber (UWOC-SMF) integrated transmission system. The proposed technique is implemented using two FBG temperature and pressure sensors fixed over diver’s suit and UWOC-SMF integrated transmission system for simultaneous local and remote monitoring of underwater temperature and pressure. Remote monitoring of underwater temperature and pressure is achieved at ship station through a remotely operated underwater vehicle (ROV) and UWOC-SMF integrated transmission system by means of shifts in the original Bragg wavelengths of sensors due to temperature and pressure variations. The performance of the sensors is analyzed for pressure and temperature in the range of 0 to 6.4 MPa (≈0 to 655 mH2O) and 40 to −2°C, respectively corresponding to different depths. The results show that the proposed technique can work well in the deep ocean over a range of pressures and temperatures of 0–7 MPa and 40 to −2°C while achieving a temperature sensitivity of 4.3 p.m./°C and a pressure sensitivity of 30.5 p.m./MPa. Clear spectra of reflected signals from FBG sensors at ship station are achieved after signal transmission over UWOC-SMF hybrid link.

Utilizing optical fiber technique to structural health monitoring of composite materials is attracting attention recently due to the inherent advantages in optical fiber sensor. However, acoustic emission signals with low energy and high frequency from transverse cracks in carbon fiber–reinforced plastic laminates are difficult to be detected by normal optical techniques. In this work, we present a phase-shifted fiber Bragg grating balanced sensing system to detect acoustic emission signals generated in a carbon fiber–reinforced plastic laminate in a three-point bending test. We demonstrated that the phase-shifted fiber Bragg grating balanced sensing system with a broad bandwidth and high sensitivity can detect high-frequency, low-energy acoustic emission signals caused by transverse cracks. In our experiments, the transverse cracks were identified very well through the detected acoustic emission signals. The relationship between the strain and the acoustic emission signals, and the typical waveforms of the acoustic emission signals were investigated. Furthermore, accurate position identification using acoustic emission detection by the phase-shifted fiber Bragg grating sensor was demonstrated. All the results obtained from the phase-shifted fiber Bragg grating sensor were compared to the results obtained from commercial lead–zirconate–titanate acoustic emission sensors. We found that the phase-shifted fiber Bragg grating balanced sensing system performance was comparable to the commercial lead–zirconate–titanate acoustic emission sensors.

Multifunctional integrated optical circuit for the fiber gyro under environmental conditionsRolf A. Regener Standard Elektrik Lorenz AG, Lorenzstr.10, D-7000 Stuttgart 40, FRGAbstractPigtailed TirLiNbO^ multifunctional inte­ grated optical circuits for use in fiber gyros have been developed and tested under environmental conditions. Emphasis has been placed on reliability of the fiber-to-wave­ guide attachment.1. IntroductionThe fiber optic gyroscope (FOG) has been and remains one of the principal elements of research and development in the field of fiber optic sensors and integrated optics technology. In general fiber optic sensors can build on know-how and components well developed for optical communication techno­ logy, e.g. semiconductor laserdiodes and de­ tectors, optical fibers and fiber components, and integrated optics. This is true although in many practical sensor systems modified or special components are required.In contrast to conventional gyroscopes the FOG is a fully electro-optical system without any moving parts. Therefore it avoids some problems of mechanical gyros such as accele­ ration sensitivity and limited measurement range. Whereas in the early years technical reasons were the incentive for research into FOG's, marketing arguments now justify the millions spent in development and preproduc- tion of fiber optic gyroscopes.The gyro market can be classified by at least two performance parameters (see Fig. 1). The gyro drift determines the lowest measurable rotation rate. Applications begin

The Army is currently investigating the potential of optical and/or hybrid optical/digital techniques to solve many of its signal processing, target identification and communications problems. It is expected that optical or hybrid optical/digital techniques will find application where large quantities of data must be processed in real time or near real time. This paper will discuss the present Army activities in acousto-, electro-, integrated and fiber optics. A few representative current applications are image and signal correlation, spectral analysis and multi-mode fiber optic systems.