Browsing by Author "Ramachandran, Siddharth"

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    Analysis of optical response of long period fiber gratings to nm-thick thin-film coatings
    Wang, Zhiyong; Heflin, James R.; Stolen, Rogers H.; Ramachandran, Siddharth (Optical Society of America, 2005-04-01)
    We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thickthin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance index-modulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thin-film coating. (C) 2005 Optical Society of America.
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    Fiber-optic sensor or modulator using tuning of long period gratings with self-assembled layers
    (United States Patent and Trademark Office, 2008-02-26)
    The provision of an ionic self-assembled multilayer (ISAM) film on a fiber-optic element including a long period grating (LPG) by a simple, room temperature process provides tuning of the LPG and/or high sensitivity to the refractive index of the ambient environment of the fiber-optic element. Inclusion of a final layer or a probe, receptor or affinity ligand in the multi-layer film provides a highly sensitive sensor for specific chemical and biological materials. Use of a turn around point (TAP) LPG allows detection to be performed by detection of light intensity rather than wavelength of attenuation. Use of a material having an electro-optical response to an electrical field by change of dimension or refractive index allows the combination of a LPG or TAP LPG and ISAM film to function as a light modulator.
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    Highly sensitive optical response of optical fiber long period gratings to nanometer-thick ionic self-assembled multilayers
    Wang, Zhiyong; Heflin, James R.; Stolen, Rogers H.; Ramachandran, Siddharth (AIP Publishing, 2005-05-01)
    Ionic self-assembled multilayers deposited on long period fiber gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Fine control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition technique for fine-tuning grating properties. In addition a variety of biological and chemical sensing agents can easily be incorporated into these films, which makes this an attractive platform for realization of high-performance LPG-based sensors. (c) 2005 American Institute of Physics.