Mid Infrared Optical Gas Sensor Using Plasmonic Mach-Zehnder Interferometer

Abstract

In this work, we propose an optimized design for on-chip gas sensor using metal-insulator (MI) plasmonic waveguide in the mid infrared range and utilizing a Mach-Zehnder Inetrferometer (MZI). The MI waveguide utilizes a high index dielectric layer on top of the metal to enhance the sensitivity of the sensor. The thickness and the refractive index of this layer are optimized to achieve high sensitivity. Using this layer, a design that exhibits high performance for both wavelength and intensity interrogation schemes is achieved. In addition, another one that furtherly enhances the sensor performance for intensity interrogation is also proposed. This design also minimizes the sensor sensitivity to wavelength variations. Intensity interrogation scheme has the advantage of eliminating the size and cost needed by wide wavelength band measurements including either spectrometer or tunable laser in wavelength interrogation. The first design sensitivity has reached 10000 nm/RIU with wavelength interrogation figure of merit (FOMλ) of 133RIU−1 and intensity interrogation FOMI of 239RIU−1. While the second one exhibit FOMI of 363RIU−1, both with length of 250 µm around 4.6 µm wavelength. Finally, these structures are cheap, compact, and easy to fabricate.