Fiber & ElectroOptics Research Center (FEORC)

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Effect Of External Index Of Refraction on Multimode Fiber Couplers
Wang, G. Z.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1995)
The dependence of the performance of fused-taper multimode fiber couplers on the refractive index of the material surrounding the taper region has been investigated both theoretically and experimentally. It has been identified that for a 2 x 2 multimode fiber coupler there is a range of output-power-coupling ratios for which the effect of the external refractive index is negligible. When the coupler is tapered beyond this region, the performance becomes dependent on the external index of refraction and lossy. To analyze the multimode coupler-loss mechanism, we develop a two-dimensional ray-optics model that incorporates trapped cladding-mode loss and core-mode loss through frustrated total internal reflection. Computer-simulation results support the experimental observations. Related issues such as coupler fabrication and packaging are also discussed. (C) 1995 Optical Society of America
Fabry-Perot Fiber-Optic Sensors in Full-Scale Fatigue Testing on an F-15 Aircraft
Kent A. M.; Gunther, Michael F.; Vengsarkar, Ashish M.; Claus, Richard O. (Optical Society of America, 1992-02-01)
We report results from fiber-optic-sensor field tests on an F-15 aircraft mounted within a full-scale test frame for the purpose of fatigue testing. Strain sensitivities of the order of 0.01 _m/m have been obtained.
Fiberoptic Temperature Sensors Based on Differential Spectral Transmittance Reflectivity And Multiplexed Sensing Systems
Wang, A.; Wang, G. Z.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1995-07-01)
A concept for optical temperature sensing based on the differential spectral reflectivity/transmittance from a multilayer dielectric edge filter is described and demonstrated. Two wavelengths, lambda(1) and lambda(2), from the spectrum of a broadband light source are selected so that they are located on the sloped and flat regions of the reflection or transmission spectrum of the filter, respectively. As temperature variations shift the reflection or transmission spectrum of the filter, they change the output power of the light at lambda(1), but the output power of the light at lambda(2) is insensitive to the shift and therefore to the temperature variation. The temperature information can be extracted from the ratio of the light powers at lambda(1) to the light at lambda(2). This ratio is immune to changes in the output power of the light source, fiber losses induced by microbending, and hence modal-power distribution fluctuations. The best resolution of 0.2 degrees C has been obtained over a range of 30-120 degrees C. Based on such a basic temperature-sensing concept, a wavelength-division-multiplexed, temperature-sensing system is constructed by cascading three sensing-edge filters that have different cutoff wavelengths along a multimode fiber. The signals from the three sensors are resolved by detecting the correspondent outputs at different wavelengths.
Layer-by-layer electrostatic self-assembly of nanoscale Fe3O4 particles and polyimide precursor on silicon and silica surfaces
Liu, Y. J.; Wang, Anbo; Claus, Richard O. (AIP Publishing, 1997-10-01)
Monolayer and multilayer ultrathin films comprised of nanosized iron oxide (Fe3O4) particles and polyimide molecules have been fabricated on single crystal silicon and quartz substrates by a novel layer-by-layer electrostatic self-assembly process. This process involves the alternate dipping of a substrate into an aqueous solution of anionic polyimide precursor (polyamic acid salt, PAATEA), followed by dipping into an aqueous solution of polycation polydiallyldimethylammonium chloride (PDDA) which coats on nanoscale Fe3O4 particles as a stabilizer. The growth process and the structure have been characterized using UV-vis spectroscopy, contact angle, and ellipsometry measurements. The results suggest that well-ordered uniform monolayer and multilayer magnetic films have been formed on silicon and silica surfaces. A recently developed highly sensitive fiber optic magnetic field sensor was used to probe the small magnetic field intensity produced by the multilayer films. (C) 1997 American Institute of Physics.
Microbend loss fiber optic direction and amplitude sensors for underwater applications
Vengsarkar, Ashish M.; Murphy, Kent A.; Tran, Tuan A.; Claus, Richard O. (Acoustical Society of America, 1990-07-01)
Dual purpose fiber optic microbend loss sensors have been developed for measurement of underwater acousticwave amplitudes and for detection of the direction of wave propagation. Three different construction schemes for cylindrical sensing elements are considered. The dual purpose hydrophones have been characterized for frequencies ranging from 15 to 75 kHz. They exhibit sensitivities in the range of -175 to -200 dB r e:1 V/uPa and directionality sensitivity limited by geometrical construction. 1990 Acoustical Society of America
Miniaturized Fiber-Optic Michelson-Type Interferometric Sensors
Murphy, Kent A.; Miller, W. V.; Tran, Tuan A.; Vengsarkar, Ashish M.; Claus, Richard O. (Optical Society of America, 1991-03-01)
We present a novel, miniaturized Michelson-type fiber-optic interferometric sensor that is relatively insensitive to temperature drifts. A fused-biconical tapered coupler is cleaved immediately after the coupled length and polished down to the region of the fused cladding, but short of the interaction region. The end of one core is selectively coated with a reflective surface and is used as the reference arm; the other core serves as the sensing arm. We report the detection of surface acoustic waves, microdisplacements, and magnetic fields. The sensor is shown to be highly stable in comparison to a classic homodyne, uncompensated Michelson interferometer, and signal-to-noise ratios of 65 dB have been obtained.
Modeling Of Fiber-Optic Sensors Based on Micromechanical Vibrations in Liquid
Prokhorov, A. M.; Claus, Richard O.; Popov, Andrey A.; Tulaikova, T. V. (Optical Society of America, 1997-08-01)
Fiber-optic chemical sensors based on optical power absorption or wavelength changes are well known. A new type of sensing element is considered. A micromechanical vibrated tiber-optic tip changes its resonance frequency during its operation. Sensors of this type are simple and convenient and do not require adjustment while in use. They are useful in industry and in medical applications. The action of this sensitive element in a liquid is considered. (C) 1997 Optical Society of America.
Optical Scanning Extrinsic Fabry-Perot Interferometer For Absolute Microdisplacement Measurement
Li, Tianchu Li; May, Russell G.; Wang, Anbo; Claus, Richard O. (Optical Society of America, 1997-02-01)
We report an optical-scanning, dual-fiber, extrinsic Fabry-Perot interferometer system for absolute measurement of microdisplacement. The system involves two air-gapped Fabry-Perot cavities, formed by fiber end faces, functioning as sensing and reference elements. Taking the scanning wavelength as an interconverter to compare the gap length of the sensing head with the reference-cavity length yields the absolute measurement of the sensing-cavity length. The measurement is independent of the wavelength-scanning accuracy, and the reference-cavity length can be self-calibrated simply by one's changing the sensing-head length by an accurate value. (C) 1997 Optical Society of America.
Sapphire Fibers: Optical Attenuation And Splicing Techniques
Barnes, Adam E.; May, Russell G.; Gollapudi, Sridhar; Claus, Richard O. (Optical Society of America, 1995-12-01)
The optical attenuation in sapphire fibers was examined. Attenuation was found to depend heavily on injection conditions. A number of techniques for making sapphire-silica fiber splices were attempted, with an effort toward optimizing injection conditions in the sapphire fiber. The most successful of these techniques, interior capillary-tube splicing, produced robust splices with an attenuation of less than 1 dB.
Split-Spectrum Intensity-Based Optical Fiber Sensors For Measurement Of Microdisplacement, Strain, And Pressure
Wang, Anbo; Miller, Mark S.; Plante, Angela J.; Gunther, Michael F.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1996-08-01)
A self-referencing technique compensating for fiber losses and source fluctuations in reflective air-gap intensity-based optical fiber sensors is described. A dielectric multilayer short-wave-pass filter is fabricated onto or attached to the output end face of the lead-in-lead-out multimode fiber. The incoming broadband light from a white light or a light-emitting diode is partially reflected at the filter. The transmitted light through the filter projects onto a mirror The light returning from the reflecting mirror is recoupled into the lead-in-lead-out fiber. These two reflections from the filter and the reflecting mirror are spectrally separated at the detector end. The power ratio of these two reflections is insensitive to source fluctuations and fiber-bending loss. However, because the second optical signal depends on the air-gap separation between the end face of the lead-in-lead-out fiber and the reflecting mirror, the ratio provides the information on the air-gap length. A resolution of 0.13 mu m has been obtained over a microdisplacement measurement range of 0-254 mu m. The sensor is shown to be insensitive to both fiber-bending losses and variations in source power. Based on this approach, a fiber-strain sensor was fabricated with a multilayer interference filter directly fabricated on the end face of the fiber. A resolution of 13.4 microstrain was obtained over a measurement range of 0-20,000 microstrain with a gauge length of 10 mm. The split-spectrum method is also incorporated into a diaphragm displacement-based pressure sensor with a demonstrated resolution of 450 Pa over a measurement range of 0-0.8 MPa. (C) 1996 Optical-Society of America

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