Optical coherence tomography (OCT) has become a useful and common diagnostic tool within the field of ophthalmology. Although presently a commercial technology, research continues in improving image quality and applying the imaging method to other tissue types. Swept-wavelength lasers based upon fiber ring cavities containing fiber Fabry-P´erot tunable filters (FFP-TF), as an intracavity element, provide swept-source optical coherence tomography (SS-OCT) systems with a robust and scalable platform. The FFP-TF can be fabricated within a large range of operating wavelengths, free spectral ranges (FSR), and finesses. To date, FFP-TFs have been fabricated at operating wavelengths from 400 nm to 2.2 µm, FSRs as large as 45 THz, and finesses as high as 30 000. The results in this paper focus on presenting the capability of the FFP-TF as an intracavity element in producing swept-wavelength lasers sources and quantifying the trade off between coherence length and sweep range. We present results within a range of feasible operating conditions. Particular focus is given to the discovery of laser configurations that result in maximization of sweep range and/or power. A novel approach to the electronic drive of the PZT-based FFP-TF is also presented, which eliminates the need for the existence of a mechanical resonance of the optical device. This approach substantially increases the range of drive frequencies with which the filter can be driven and has a positive impact for both the short all-fiber laser cavity (presented in this paper) and long cavity FDML designs as well.
One of the most common fiber optic sensor (FOS) types used are fiber Bragg gratings (FBG), and the most frequently measured parameter is strain. Hence, FBG strain sensors are one of the most prevalent FOS devices in use today in structural sensing and monitoring in civil engineering, aerospace, marine, oil and gas, composites and smart structure applications. However, since FBGs are simultaneously sensitive to both temperature and strain, it becomes essential to utilize sensors that are either fully temperature insensitive or, alternatively, properly temperature compensated to avoid erroneous measurements. In this paper, we introduce the concept of measured “total strain”, which is inherent and unique to optical strain sensors. We review and analyze the temperature and strain sensitivities of FBG strain sensors and decompose the total measured strain into thermal and non-thermal components. We explore the differences between substrate CTE and System Thermal Response Coefficients, which govern the type and quality of thermal strain decomposition analysis. Finally, we present specific guidelines to achieve proper temperature-insensitive strain measurements by combining adequate installation, sensor packaging and data correction techniques.
Given the growing demand for oil and natural gas to meet the world's energy needs, there is nowadays renewed interest
in the use of liquefied natural gas (LNG) systems. For LNG to remain in its liquid phase, the gas has to be kept at
cryogenic temperatures (< 160°C). And, as part of the LNG supply process, it becomes necessary to transport it using
massive carrier tankers with cargo hulls operating at low temperatures and using special insulating double-wall
construction. The safe and reliable storage and transportation of LNG products calls for low temperature monitoring of
said containers to detect the onset of any potential leaks and possible thermal insulation degradation. Because of the
hazardous nature of this cargo, only intrinsically-safe, explosion proof devices can be used. Optical fiber sensors-- such
as fiber Bragg gratings-- are ideal for this application given their dielectric nature and multi-point sensing telemetry
In this paper, we describe the development of an on-line, multi-point FBG-based low temperature monitoring system
based on a network of specially packaged FBG temperature and strain sensors mounted at critical locations within the
inner hull, cofferdam and secondary barriers of a LNG carrier tanker. Given the stringent cryogenic operating
temperature conditions, pertinent FBG designs, coatings and packaging approaches were formulated along with adequate
installation techniques and integration of the interrogating FBG electronics into the tanker's overall SCADA monitoring
system. FBG temperature sensors were demonstrated to be stable and sensitive over the 80-480K range. Stability is ±
0.25K or better with repeated calibrations, and long term stability at 480K is ~0.2mK/hour.
Long-gauge SOFO sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & Fiber optic sensing systems are increasingly recognized as a very attractive choice for structural health monitoring. Moving form demonstration project to industrial applications requires an integrated approach where the most appropriate technologies are combined to meet the user's requirements. In this context it is often necessary and desirable to combine different sensing technologies in the same project. A bridge-monitoring project might for example require long-gauge interferometric sensors to monitor the concrete deck, interferometric inclinometers for the piles and fiber Bragg grating sensors for the monitoring of the strains in the steel beams and for measuring temperatures. Although fiber optic sensors relying on different technologies can easily be combined at the packaging and cable levels, they often require dedicated instruments to be demodulated. A unified demodulation system would therefore be very attractive.
This paper describes a technique relying on the analysis of reflected spectra and allowing the demodulation of interferometric (Michelson or Faby-Perot) sensors and fiber Bragg grating sensors with a single measurement system. It also compares the obtained performance in terms of resolution and dynamic range with the available dedicated systems.
Conference Committee Involvement (2)
Fiber Optic Sensors and Applications XV
17 April 2018 | Orlando, Florida, United States
Fiber Optic Sensors and Applications XIV
11 April 2017 | Anaheim, California, United States