Abstract
We propose and demonstrate a cost-effective liquid refractive index (RI) sensor in polymer materials by employing a Mach-Zehnder interferometer (MZI) formed with the conventional strip waveguide. The proposed sensor can attain high sensitivity by choosing a suitable reference arm length to reduce optical path difference (OPD) between the two arms of the employed MZI. Our fabricated devices, which have the same sensing arm length of 7900 µm but different reference arm lengths of 7900.0, 7942.5, 7950.9, 7962.2, and 7969.5 µm, respectively, exhibit the maximum RI sensitivities of 33662.8 nm/RIU, and almost the same detection range (DR) of 0.0041 ± 0.0002 RIU.
Highlights
Over the past decades, optical waveguide liquid refractive index (RI) sensors have received more and more attention as an increasingly important tool in biochemical analysis applications by virtue of their unique advantage enabling high-sensitive, real-time, and label-free detection [1]
A simple asymmetric Mach-Zehnder interferometer (MZI) formed with the conventional strip waveguide is employed, in which the reference arm length and the optical path difference (OPD) between the two arms is optimized to attain a high sensitivity
After the BCB layer was fully cured, the designed MZI pattern was realized by the standard photolithography and transferred into BCB film by the inductively coupled plasma (ICP) etching with the mixture gases of Ar and CF4
Summary
Optical waveguide liquid refractive index (RI) sensors have received more and more attention as an increasingly important tool in biochemical analysis applications by virtue of their unique advantage enabling high-sensitive, real-time, and label-free detection [1]. As the MZI-based sensors utilize evanescent field probing scheme, to enhance light-analyte interactions and to achieve large waveguide sensitivity, strong penetration of the evanescent field into the analyte is required To this end, some novel waveguides, including plasmonic waveguide [10], slot waveguide [11], hybrid plasmonic waveguide [12],[13], subwavelength grating slot waveguide [14], and the waveguide with metal under-cladding [15], have been proposed and evaluated during the past years. The motivation of this work is to develop a cost-effective liquid RI sensor in polymer materials To this end, a simple asymmetric MZI formed with the conventional strip waveguide is employed, in which the reference arm length and the OPD between the two arms is optimized to attain a high sensitivity. Our proposed MZI sensor is costeffective because of its structural simplicity, easy processing, and mass fabrication capability
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