Simi Valley, CA, United States
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Evert A.,Clemson University | James A.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | And 6 more authors.
Optics Express | Year: 2012

Optical fibers have become ubiquitous tools for the creation, propagation, manipulation, and detection of light. However, while the intensity of light propagating through the fiber can increase or decrease along the length through amplification or attenuation, respectively, the properties of the fiber itself generally do not, thus removing an opportunity to further control the behavior of light and performance of fiber-based devices. Shown here are optical fibers that exhibit significant changes in their longitudinal optical properties, specifically a tailored longitudinal numerical aperture change of about 12% over less than 20 meters of length. This is about 1900 times greater than previously reported. The Brillouin gain coefficient was found to decrease by over 6 dB relative to a standard commercial single mode fiber. Next generation analogs are expected to exhibit more than a 10 dB reduction in SBS gain using larger, yet still reasonably manufacturable gradients over practical lengths. © 2012 Optical Society of America.


Dragic P.D.,University of Illinois at Urbana - Champaign | Ballato J.,Clemson University | Morris S.,Clemson University | Evert A.,Clemson University | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Optical fiber sensors utilizing Brillouin scattering rely on the principle that the Brillouin frequency shift is a function of the local temperature or strain. Conventional optical fibers, such as standard telecommunications single-mode fibers, have been successfully used in these applications, and most typically in the time domain, such as with BOTDR. Such conventional fibers however are susceptible simultaneously to both temperature and strain, requiring either at least two fibers or specialized cabling to distinguish the effects of a local stress from those of a local change in temperature. Recently, methods utilizing fibers possessing at least two Brillouin frequency shifts, each with different temperature or strain coefficients have been proposed. However, realizing such fibers is challenging, requiring fibers with regions of very different compositions, all of which must have substantial overlap with the optical field, posing significant manufacturing challenges. We present several new specialty optical fibers based on novel and unconventional fabrication techniques with significant potential for use in distributed fiber sensor systems. First, we describe a class of fibers fabricated from materials whose Brillouin frequency shifts are immune to either temperature or strain, with a demonstration of the former using fiber derived from sapphire crystal, and modeling and measurements predicting the latter. The 'Brillouin-athermal' fiber enables the measurement of a local strain, independent of the local temperature. Second, we describe and demonstrate a novel group of longitudinallygraded (chirped) fibers enabling easily-implemented frequency-domain systems; affording the potential to simplify and reduce the cost of Brillouin-based distributed sensors. © 2013 SPIE.


Ballato J.,Clemson University | McMillen C.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | And 4 more authors.
Optical Materials Express | Year: 2012

Described herein are glass-clad optical fibers, fabricated using a molten core fiber draw process, comprising oxide cores in the Bi2O3-GeO2 system. More specifically, the fibers utilized a borosilicate glass cladding with core compositions in the initial preform ranging from un-reacted crystalline Bi2O3-rich (Bi2O3 + GeO2) powders to stoichiometric crystalline Bi12GeO20. Fibers drawn from the as-purchased crystalline Bi2O3-rich powders were amorphous with a transmission of about 80% at 1.3 μm. Fibers drawn from the crystalline Bi12GeO20 core contained a mixture of crystalline bismuth germanate (Bi2GeO5) and bismuth oxide (δ-Bi2O3/BiO2-x). While representing an initial proof-of-concept, this work shows that commercially-relevant draw processing can be employed to yield fibers with core composition that are very difficult to fabricate using conventional methods and that the molten core method further enables in situ reactive chemistry to take place during fiberization resulting in amorphous or crystalline oxide core fibers depending on initial core composition. Perhaps more importantly is that optical fibers possessing acentric, hence optically nonlinear, oxide crystals can be realized in a scalable manufacturing manner though further optimization is required both of the core chemistry and process conditions in order to achieve a single phase and single crystalline fiber. © 2012 Optical Society of America.


Ballato J.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | Morris S.,Clemson University | And 3 more authors.
Optics Letters | Year: 2011

Silica-clad optical fibers comprising a core of crystalline germanium were drawn using a molten core technique. With respect to previous fibers drawn using a borosilicate cladding, the present fibers exhibit negligible oxygen despite being fabricated at more than twice the melting point of the germanium. The counterintuitive result of less oxygen when the fiber is drawn at a higher temperatures is discussed. The measured propagation loss for the fiber was 0.7dB/cm at 3.39μm, which is the lowest loss reported to date. © 2011 Optical Society of America.


Morris S.,Center for Optical Materials Science and Engineering Technologies | Hawkins T.,Center for Optical Materials Science and Engineering Technologies | Foy P.,Center for Optical Materials Science and Engineering Technologies | Ballato J.,Center for Optical Materials Science and Engineering Technologies | And 2 more authors.
International Journal of Applied Glass Science | Year: 2012

Glass-clad optical fibers comprising a crystalline semiconductor core have garnered considerable recent attention for their potential utility as novel waveguides for applications in nonlinear optics, sensing, power delivery, and biomedicine. To date, cladding compositions have relied on commercially-available expedients and have not been tailored for the specific semiconductor core nor the application. In this work, more-optimum silicate and nonoxide glass compositions are developed for unary (Si, Ge), binary (InSb, GaAs), and ternary (GaAlSb) semiconductor cores based on two main design criteria: (1) matching the thermal expansion coefficient between semiconductor core and glass cladding and (2) matching the viscosity-temperature dependences such that the cladding glass draws into fiber at a temperature slightly above the melting point of the semiconductor. While this latter requirement is critical to the molten core fabrication method, which offers a practical approach to long fiber lengths at acceptable manufacturing speeds (>m/s), these compositions are more broadly applicable to other semiconductor fiber processing methods. Preliminary experimental results on silicon core optical fiber are provided and show a marked diminution in oxygen content relative to analogous fibers drawn using a pure silica cladding. © 2012 The American Ceramic Society and Wiley Periodicals, Inc.


McMillen C.,Clemson University | Brambilla G.,University of Southampton | Morris S.,Clemson University | Hawkins T.,Clemson University | And 5 more authors.
Optical Materials | Year: 2012

Previously reported [Opt. Mater. 32 (2010) 862-867] was the crystallographic orientation of the core phase in a semiconductor optical fiber relative to the fiber axes. In this continuation, the same glass-clad crystalline germanium core optical fibers were tapered and, for the first time to the best of our knowledge, the influence of tapering on the core crystallography is studied and reported. Single crystal X-ray diffraction (SC-XRD) shows that the act of tapering not only modifies the fiber dimension but also re-orients the crystallography of the crystalline core. This can be especially useful to the continued optimization of these crystalline semiconductor core optical fibers and such control over crystal orientation is critical for future fiber-based nonlinear and optoelectronic devices. © 2012 Elsevier B.V. All rights reserved.


Morris S.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | Mcmillen C.,Clemson University | And 5 more authors.
Optical Materials Express | Year: 2011

Silicon optical fibers fabricated using the molten core method possess high concentrations of oxygen in the core [Opt. Express 16, 18675 (2008)] due to dissolution of the cladding glass by the core melt. The presence of oxygen in the core can influence scattering, hence propagation losses, as well as limit the performance of the fiber. Accordingly, it is necessary to achieve oxygen-free silicon optical fibers prior to further optimization. In this work, silicon carbide (SiC) is added to the silicon (Si) core to provide an in situ reactive getter of oxygen during the draw process. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and powder x-ray diffraction (P-XRD) are used to verify that the glass-clad silicon optical fibers possess very low oxygen concentrations and that the SiC is consumed fully during the reactive molten core fabrication. Optical measurements indicated a reduction in light scattering out of the silicon core as expected. However, the measured attenuation of about 10 dB/cm, which is consistent with existing low-oxygen-content silicon fibers, implies that scattering might not be the dominant source of loss in these molten core-derived silicon fibers. More generally, this work shows that the high temperature processing of optical fibers can be an asset to drive chemical reactions rather than be limited by them. © 2011 Optical Society of America.


Morris S.,Clemson University | McMillen C.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | And 3 more authors.
Journal of Crystal Growth | Year: 2012

Crystalline semiconductor core optical fibers have received growing attention as greater understanding of the underlying materials science, coupled with advances in fiber processing and fabrication, have expanded the quality and portfolio of available materials. In a continued effort to better understand the nature of the crystal formation this work studies the role of the cross-sectional geometry on the resultant core crystallography with respect to the fiber axis. More specifically, a molten-core approach was used to fabricate silicon optical fibers clad in silica tubes of either circular or square inner cross-sections. In both geometric cases, the silicon core was found to possess regions of single crystallinity where specific crystal orientations persisted along a fiber length of about 4-5 mm prior to transitioning through polycrystalline regions. However, the rotation and tilting angular combination needed to align a given crystallographic axis with the fiber axis was more constant over the single crystalline region in the case of the square-core fiber while more significant variations were observed in the round-core case. This work begins to elucidate some of the microstructural features, not present in conventional glass optical fibers, that could be important for future low-loss single crystalline semiconductor optical fibers. © 2011 Elsevier B.V.


Morris S.,Clemson University | Hawkins T.,Clemson University | Foy P.,Clemson University | Hudson J.,Clemson University | And 4 more authors.
Optical Materials Express | Year: 2012

Glass clad semiconductor core fibers have received much attention recently for their potential utility for nonlinear optics and infrared power delivery. As these fibers have progressed, it has become evident that a greater understanding as to the dominant sources of loss is needed. This work begins that discussion by investigating intrinsic and extrinsic sources of loss in silica glass clad crystalline silicon core optical fibers. Of particular interest are, to the best of our knowledge, the first lattice-fringe images of single and poly-crystalline regions of the silicon core optical fibers as well as scattering sources. Suggested herein are methods to further reduce the presence of impurities and defects that lead to scattering and dominate optical losses. © 2012 Optical Society of America.


Gupta N.,Clemson University | McMillen C.,Clemson University | Singh R.,Clemson University | Podila R.,Clemson University | And 8 more authors.
Journal of Applied Physics | Year: 2011

The recent realization of silicon core optical fibers has the potential for novel low insertion loss rack-to-rack optical interconnects and a number of other uses in sensing and biomedical applications. To the best of our knowledge, incoherent light source based rapid photothermal processing (RPP) was used for the first time to anneal glass-clad silicon core optical fibers. X-ray diffraction examination of the silicon core showed a considerable enhancement in the length and amount of single crystallinity post-annealing. Further, shifts in the Raman frequency of the silicon in the optical fiber core that were present in the as-drawn fibers were removed following the RPP treatment. Such results indicate that the RPP treatment increases the local crystallinity and therefore assists in the reduction of the local stresses in the core, leading to more homogenous fibers. The dark current-voltage characteristics of annealed silicon optical fiber diodes showed lower leakage current than the diodes based on as-drawn fibers. Photons in UV and vacuum ultraviolet (VUV) regions play a very important role in improving the bulk and carrier transport properties of RPP-treated silicon optical fibers, and the resultant annealing permits a path forward to in situ enhancement of the structure and properties of these new crystalline core optical fibers. © 2011 American Institute of Physics.

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