Laser-written Mach Zehnder interferometer in silica with surface-written sensing arms and sub-micron thick doped-polymer film for increased evanescent field interferometric methane sensing

George T. Ong; Timothy Lee; Martynas Beresna; Sam McQuillan; Rand Ismaeel; Gilberto Brambilla

doi:10.1117/12.2653541

17 March 2023 Laser-written Mach Zehnder interferometer in silica with surface-written sensing arms and sub-micron thick doped-polymer film for increased evanescent field interferometric methane sensing

George T. Ong, Timothy Lee, Martynas Beresna, Sam McQuillan, Rand Ismaeel, Gilberto Brambilla

Author Affiliations +

Proceedings Volume 12409, Laser-based Micro- and Nanoprocessing XVII; 1240917 (2023) https://doi.org/10.1117/12.2653541
Event: SPIE LASE, 2023, San Francisco, California, United States

Abstract

Femtosecond laser writing offers low-cost and straightforward photonic circuit fabrication compared to planar cleanroom silicon photonics. Here, we propose a compact and robust laser-written methane gas sensor based on a Mach Zehnder interferometer (MZI) in silica. The MZI is to be written in a 1 x 1cm bulk fused silica substrate with the sensing arm adjacent to the glass surface to allow evanescent field interaction with its environment. The optimisation of a styrene acrylonitrile (SAN polymer, n=1.56) surface film is simulated and discussed. Offering enhanced evanescent field in the sensing arm and selectivity to methane. Demonstrations of fabrication of low-stress buildup multi-scan waveguides and directional couplers is presented. The cladding layer thickness is engineered to improve the evanescent field ratio (power in sensitized SAN region to the total mode power) in the sensing arm up to 15% from previously documented laser written MZI sensors, thus overcoming limitations imposed by the low laser-induced index. Surface waveguides are written adjacent to the surface of the sample, improving previously achieved surface proximity for high index waveguides. The proposed sensor will require one writing step, one spin-coating step and the waveguide is mode-matched well to integrate with SMF-28 fibre devices. The sensitive polymer layer could easily be developed for other analytes with sensitivities estimated to be as comparable to similar devices developed on a silicon nitride cleanroom.

Conference Presentation

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George T. Ong, Timothy Lee, Martynas Beresna, Sam McQuillan, Rand Ismaeel, and Gilberto Brambilla "Laser-written Mach Zehnder interferometer in silica with surface-written sensing arms and sub-micron thick doped-polymer film for increased evanescent field interferometric methane sensing", Proc. SPIE 12409, Laser-based Micro- and Nanoprocessing XVII, 1240917 (17 March 2023); https://doi.org/10.1117/12.2653541

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