A fiber optic surface plasmon resonance sensor is described. Experimental results are presented which demonstrate a resolution of approximately 8 by 10-5 refractive index units for this system. The detection of heavy metal Cu and Pb ions in solutionis demonstrated using the SPR sensor as the working electrode in an anodic stripping voltammetry experiment.
An Erbium amplified spontaneous emission (ASE) source is described and test results are presented. The ASE output power, spectrum, coherence, relative intensity noise (RIN), and polarization were measured for three different Erbium doped fibers of various lengths. Output powers up to 15 mW were achieved with 70 mW of 980 nm pump power. Measurement of the ASE coherence resulted in 0.5 mm at the -30 dB level while the RIN was measured to be < -125 dB/rt- Hz. The coherence and noise characteristics of this source match specifications for a low noise fiber optic gyroscope and since the source design is simple, a low cost Erbium ASE source can be built.
This paper outlines recent progress made by Optiphase Inc.in the development of low-cost, high performance interferometric demodulators applied to multi-channel interrogation. The paper's focus is on the Optiphase digital demodulation concept applied first for single channel operation and then to multi-channel operation. This paper also presents single and multi-channel demodulation test data taken from hardware developed for these applications.
The design and test result of an ultra miniature interferometric fiber optic rate gyro (IFOG) are reported. A unique IFOG gyro has been fabricated and tested. The gyro implements low cost components packaged in a volume less than 2.3 cubic inches including electronics. Test results verify that operational performance requirements over the temperature range of -57 to +71 C are met in the design. Key results include: electronic power consumption of 2.3 Watts, noise < 0.16 deg/sec/rt-Hz, scale factor of 32.9 mV/deg.sec, activation time of < 300 msec, threshold and resolution of 0.01 deg/sec, scale factor linearity error < 0.14 percent, and bias < 0.1 deg/sec. The gyro also survived a vibration test at 26.5 Grms. The gyro design is presented and accompanied with test data showing general conformance to the design's operational performance requirements.
Strains produced in the core of a multi-parameter Bragg grating sensor by transverse loading, axial loading or a uniform temperature change are computed by finite element analyses. The sensor is formed by writing gratings at two wavelengths in polarization maintaining fiber in which birefringence in the core is induced by an elliptical stress applying region. The finite element model accounts for the differences in geometry and mechanical properties of the different regions of the fiber. The computed strains are needed to determine the elements of a matrix that relates wavelength shifts of Bragg peaks to axial strain, two components of transverse strain and temperature change.
This paper overviews recent progress made on the development of a 3 axis fiber optic strain sensor that has the potential to measure temperature as well. Initial efforts have been conducted to demonstrate the performance potential of an approach using dual overlaid fiber gratings written at 1300 and 1550 nm written onto conventional polarization maintaining fiber. This paper reports on some of the results of this study and indicates the direction of future efforts to develop a multiplexable, single point three axis strain and temperature fiber grating sensor.
A neutron spectrometer is a device that measures the spectrum of the kinetic energy of neutrons. There are numerous applications that can profitably use a compact neutron spectrometer. For instance, fast neutron resonance radiography requires sufficiently high resolution (several percent) to identify the absorption spectra of carbon, nitrogen and oxygen nuclei for incident neutrons in the thermal to 5 MeV range. In the nuclear arms-control arena, a device that can collect neutron spectral information without revealing design information would have considerable value for treaty verification. Conventional neutron spectrometers operate on a time-of-flight (TOF) basis. Neutrons of interest range in energy from thermal energy (0.025 eV) to a few MeV for special nuclear material and from ca. 100 KeV to 5 MeV for identification of explosives. A thermal neutron has a speed of ca. 2,000 mis; a 1 MeV neutron has a speed of ca. 13,000 km/sec. A TOF spectrometer has a series of choppers, each turning at different speeds, that pass only those neutrons in a given energy (velocity) range; the velocity cohort that is allowed to pass through the spectrometer and be counted is selected by varying the relative speeds ofrotation. Thus, the TOF spectrometer is, by necessity, large (meters to tens of meters). In addition, only a small fraction of all the incident neutrons are measured during any given time interval. That is, the TOF spectrometer makes very inefficient use of the neutron flux. We will describe a spectrometer that has been made practical by the development of neutron-sensitive scintillating fibers. 1-s This concept is "work-in-progress" but the results of a simple theoretical test are reported here.
A simple, potentially low cost fiber grating demodulation is described that can be used to measure very fast strain events. The unit consists of a broadband light emitting diode light source that is used to illuminate a fiber grating. The narrow band reflected light signal is directed toward a broadband chirped fiber grating whose transmission and reflection is monitored by a pair of receivers. The ratioed output can be used to monitor fast events. An example of using this sensor to support impact testing is given.
The development of a rugged optical fiber telemetry system for coiled-tubing earth-drilling is described. The transmitter and receiver of the telemetry system are located on the surface. A high temperature fiber cable connects a serial array of downhole modulators with the surface. Each modulator consists of an intrinsic fiber Bragg grating (FBG) fixed to a piezoelectric transducer (PZ). Each modulating signal causes a PZ to stretch its attached FBG, shifting the wavelength of the light reflected by the grating. The wavelength shift of the grating-reflected light is detected at the output using a Mach-Zehnder interferometer.
The use of a focused ion beam (FIB) to fabricate novel fiber optic structures is described. Using a FIB in either the ion milling mode or deposition mode a large variation in the index of refraction may be introduced in the optical fiber. With a potential beam size as small as 0.02 micrometers , the FIB process provides the ability to both expand the variety and reduce the size of structures that maybe embedded in optical fiber. For example, estimates indicate that a 20 groove Bragg grating coupled to 10 percent of the guided more energy can achieve a maximum 98 percent reflectivity. CUrrent drawbacks of the FIB process include slow production time and high production cost.
Current sensors for monitoring web manufacturing processes generally provide only point measurements with the result that a very small area of the web is actually characterized. This paper describes a new web sensing concept based upon the use of a distributed fiber optic detector.
While fiber optic Bragg gratings sensors have emerged as a viable commercial product they possess the inherent inflexibility that once written, the nonstressed gratin spacing is fixed. We have begun to explore an alternative method of fabricating Bragg sensors - one where you have a single fiber optic Bragg grating sensor, but where you are able to write your own grating prior to parameter measuring with the broadband light source. In this alternative, a photosensitive fiber core material exists at the FBGS sensing 'site' along the fiber. THe diffraction grating is written via a deliberate intensity variation in the light which is injected into the fiber. The slight difference in refractive index between the photogrey section of the core and the 'regular' fiber causes an internal Fabry-Perot resonator cavity to be established. The intensity-modulated high power laser bit stream reflects back and forth within this cavity establishing a standing wave pattern. This pattern may be varied, and hence the grating spacing is variable, by changing the high power laser's bit pattern. This standing wave pattern effectively illuminates the photogrey section nonuniformly with the high power portions of the standing wave pattern causing more darkening - thereby in essence creating the Bragg diffraction grating.
The use of chloride-based deicing agents to help clear US highways of roadway hazards leads to associated chemical related problems. Fouling of local rivers and streams due to runoff of the water borne chlorides is significant and has contributed to local ordances are attempting to force state agencies to reduce, if not eliminate, the use of these chlorides. With respect to the corrosion aspects of chloride application, cracks that occur in the roadway/bridge pavement allow water to seep into the pavement carrying the chloride to the rebar with the resultant increase in corrosion. The costs of this corrosion are considerable and have led to the widespread use of chloride/water impermeable membranes on roadways and especially within bridges. Fiber optic sensor have repeatedly been shown to provide measurement capabilities of parameters within such reinforced concrete structures. Development of a fiber optic chloride sensors capable of being embedded within a roadway or bridge deck is reported.
We present recent work on fiber optic sensor systems for structural element characterization and monitoring. One particular application area currently under study is the characterization and testing of pultruded composite beams. The motivation behind this project and current status is described. Fiber optic sensor systems to suit the application have been developed. In particular, the development of both AO tunable filter and all-fiber passive demodulation schemes for in-fiber Bragg grating sensors is described.
Researchers throughout the world have successfully developed embedded long-lived silica-based fiber optic sensors for the performance and health monitoring of reinforced concrete structures. We have examined the user of polymer optical fiber (POF) as the base material for fiber optic sensors which are to be embedded into concrete structures. Such POF sensors hold the possibility for considerably reduced expense both in terms of actual component costs and, perhaps more importantly, in the relative ease with which such sensor may be embedded into concrete structures. Results of our laboratory and field studies, where POF sensors were embedded into an in-service railroad bridge, are discussed.
Speckle based fiber optic sensors have been developed and used in laboratory and field settings for a number of years. In the case of speckle-based fiber optic vibration sensor, optical signal processing of the field emerging form a multimode fiber has been performed through the use of intensity modulating masks. In such cases, portions of the speckle pattern are not allowed to illuminate a photodetector thereby performing forms of statistical selection of modal patterns. While this technique is robust, it does inherently reduce the sensor's operational dynamic range, and signal-to-noise ratio, due to the simple fact that a portion of the light field is not used. By contrast, it is possible to use phase-contrast enhancing techniques found in microscopy to phase-modulate the fiber's speckle pattern. The performance of a multimode fiber optic sensor using these techniques is compared with the more traditional intensity-modulating fiber optic sensor.