Wavelength tunable long period gratings based on silica waveguide geometric modulation

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DOIResolve DOI: http://doi.org/10.1117/12.874696
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Proceedings titleSPIE - International Society for Optical Engineering. Proceedings
ConferenceOptical Components and Materials VIII, 25 January 2011 through 26 January 2011, San Francisco, CA
Article number79340T
SubjectLong Period Gratings; optical coupling; silica-on-silicon; surface corrugation; waveguide array; Cladding (coating); Diffraction gratings; Fiber optic sensors; Fluorine containing polymers; Germanium; Light refraction; Modulation; Periodic structures; Photolithography; Photosensitivity; Planar waveguides; Plasma filled waveguides; Polymers; Reactive ion etching; Refractive index; Refractometers; Signal processing; Silicon oxides; Silica
AbstractThis paper presents planar long period grating (LPG) devices based on a periodic thickness variation in the waveguide core, fabricated by etching into the lower cladding layer prior to definition of the waveguide layer. This periodic geometric change results in a stable grating structure and a permanent refractive index modulation of 10 -4 or higher, which is comparable to the index modulation in Ge-doped silica material induced by photo irradiation techniques widely used in fiber grating fabrication. This grating produces a strong resonance at a particular wavelength in the transmission spectrum, enabling a range of applications from wavelength filtering to signal distribution in communication networks. In this work, a polymer and silica hybrid architecture has been implemented in order to achieve wavelength tunability. Using a thermally oxidized silicon layer as a lower cladding, a Ge-doped silica ridge is patterned using conventional photolithography and reactive ion etching to form the waveguide core, which is then covered with a low index fluorinated polymer cladding. While the silica waveguides offer a lower propagation loss and an easy processability, the top polymer allows the device to be thermally tuned over a wide wavelength range by exploiting the opposite thermo-optic coefficient between fluorinated polymer and silica, and the high sensitivity of the underlying LPG to the refractive index of the cladding layer. Strong rejection bands have been demonstrated in the C+L band, in good agreement with theoretical calculations. Corrugated structures have been defined across an extended area under multiple waveguides resulting in coupling of light from the fundamental mode into cladding modes and back into the neighboring waveguides located far from the evanescent coupling distance. This kind of coupler can facilitate devices that require extraction and control of a particular waveguide mode for applications such as multiple channel signal distribution and temporal pulse shaping. Implementation of LPGs for these applications will be discussed. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
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AffiliationNational Research Council Canada (NRC-CNRC); NRC Institute for Chemical Process and Environmental Technology (ICPET-ITPCE)
Peer reviewedYes
NPARC number21271162
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Record identifieree97b15f-8c1a-4c6d-bae9-3541048cfb79
Record created2014-03-24
Record modified2017-04-24
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