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Capability for Fine Tuning of the Refractive Index Sensing Properties of Long-Period Gratings by Atomic Layer Deposited Al2O3 Overlays
Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Koszykowa 75, Warsaw 00-662, Poland
Centre de Recherche en Photonique, Université du Québec en Outaouais, 101 rue Saint-Jean-Bosco, Gatineau, QC J8X 3X7, Canada
Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw 02-666, Poland
* Author to whom correspondence should be addressed.
Received: 4 October 2013; in revised form: 5 November 2013 / Accepted: 9 November 2013 / Published: 28 November 2013
Abstract: This work presents an application of thin aluminum oxide (Al2O3) films obtained using atomic layer deposition (ALD) for fine tuning the spectral response and refractive-index (RI) sensitivity of long-period gratings (LPGs) induced in optical fibers. The technique allows for an efficient and well controlled deposition at monolayer level (resolution ~ 0.12 nm) of excellent quality nano-films as required for optical sensors. The effect of Al2O3 deposition on the spectral properties of the LPGs is demonstrated experimentally and numerically. We correlated both the increase in Al2O3 thickness and changes in optical properties of the film with the shift of the LPG resonance wavelength and proved that similar films are deposited on fibers and oxidized silicon reference samples in the same process run. Since the thin overlay effectively changes the distribution of the cladding modes and thus also tunes the device’s RI sensitivity, the tuning can be simply realized by varying number of cycles, which is proportional to thickness of the high-refractive-index (n > 1.6 in infrared spectral range) Al2O3 film. The advantage of this approach is the precision in determining the film properties resulting in RI sensitivity of the LPGs. To the best of our knowledge, this is the first time that an ultra-precise method for overlay deposition has been applied on LPGs for RI tuning purposes and the results have been compared with numerical simulations based on LP mode approximation.
Keywords: optical fiber sensors; refractive index sensor; long-period gratings (LPG); Atomic Layer Deposition (ALD); thin films; optical properties; aluminum oxide (Al2O3)
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Śmietana, M.; Myśliwiec, M.; Mikulic, P.; Witkowski, B.S.; Bock, W.J. Capability for Fine Tuning of the Refractive Index Sensing Properties of Long-Period Gratings by Atomic Layer Deposited Al2O3 Overlays. Sensors 2013, 13, 16372-16383.
Śmietana M, Myśliwiec M, Mikulic P, Witkowski BS, Bock WJ. Capability for Fine Tuning of the Refractive Index Sensing Properties of Long-Period Gratings by Atomic Layer Deposited Al2O3 Overlays. Sensors. 2013; 13(12):16372-16383.
Śmietana, Mateusz; Myśliwiec, Marcin; Mikulic, Predrag; Witkowski, Bartłomiej S.; Bock, Wojtek J. 2013. "Capability for Fine Tuning of the Refractive Index Sensing Properties of Long-Period Gratings by Atomic Layer Deposited Al2O3 Overlays." Sensors 13, no. 12: 16372-16383.