8 March 2014 Sensitivity of Mach-Zehnder interferometer for dissolved gas monitoring
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An integrated optical sensor is developed for measuring gas concentration for subsea and atmospheric applications. The optical sensor is based on a waveguide Mach-Zehnder interferometer (MZI). In MZI, the light is spilt into a sensing and a reference arm and after a certain distance the branches are recombined. The sensing branch is covered with a sensitive layer that has high affinity towards a specified gas. The presence of the gas gives a change in the refractive index of the sensing arm, which is translated into a change in the output signal. With a prior calibration, the change in the output signal is correlated to the gas concentration. The waveguide should be single-mode and it is desirable to have high intensity in the evanescent field. By using a high refractive index material and a thin waveguide core, the intensity of the evanescent field can be enhanced. Simulations are performed to obtain waveguide parameters with low losses and high sensitivity. The maximum sensitivity at wavelength 785 nm was obtained for a waveguide of core thickness 150 nm, rib height 5 nm and width 1 m for TM polarization. The first measurements of phase sensitivity of 12456π rad/RIU was obtain by the Hydrogen Chlorine (HCl) measurement. This is comparable to the phase sensitivity of 14268π rad/RIU obtained by the simulation.μ
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Susan Lindecrantz, Susan Lindecrantz, Firehun T. Dullo, Firehun T. Dullo, Balpreet S. Ahluwalia, Balpreet S. Ahluwalia, Olav G. Hellesø, Olav G. Hellesø, "Sensitivity of Mach-Zehnder interferometer for dissolved gas monitoring", Proc. SPIE 8988, Integrated Optics: Devices, Materials, and Technologies XVIII, 898818 (8 March 2014); doi: 10.1117/12.2039431; https://doi.org/10.1117/12.2039431

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