Abstract
The cladding-modified long-period-grating (LPG) refractive-index sensors with a high-refractive-index overlay
are optimized based on systematical studies on the structure-modified LPG. Dependence of the cladding-mode effective
indexes on the parameters of the structure-modified LPG, such as the overlay refractive index (RI), the overlay
thickness, the cladding-layer radius, and the ambient RI, as well as the order of cladding mode, are investigated in
detail. An optimization procedure based on reducing the cladding radius, keeping the grating period as an adaptive
parameter, and employing the HE<sub>13</sub> mode
notch-wavelength shift is proposed for the LPG RI sensors. By using the proposed optimization method, it is shown
that an ambient RI sensitivity as large as 5980 nm/RI can be achieved, representing a threefold sensitivity
enhancement, as compared to the best result obtained from the reported structure, in which the high
HE<sub>17</sub> mode resonate notch wavelength was employed in
sensing.
© 2007 IEEE
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