*Article* **Elimination of Unwanted Modes in Wavelength-Selective Uncooled Infrared Sensors with Plasmonic Metamaterial Absorbers using a Subtraction Operation**

#### **Shinpei Ogawa 1,\*, Yousuke Takagawa 2 and Masafumi Kimata 2**


Received: 3 September 2019; Accepted: 25 September 2019; Published: 27 September 2019

**Abstract:** Wavelength- or polarization-selective uncooled infrared (IR) sensors have various applications, such as in fire detection, gas analysis, hazardous material recognition, biological analysis, and polarimetric imaging. The unwanted modes originating due to the absorption by the materials used in these sensors, other than plasmonic metamaterial absorbers (PMAs), cause serious issues by degenerating the wavelength or polarization selectivity. In this study, we demonstrate a method for eliminating these unwanted modes in wavelength- or polarization-selective uncooled IR sensors with various PMAs, using a subtraction operation and a reference pixel. The aforementioned sensors and the reference pixels were fabricated using a complementary metal oxide semiconductor and micromachining techniques. We fabricated the reference pixel with the same structure as the PMA sensors, except a flat mirror was formed on the absorber surface instead of PMAs. The spectral responsivity measurements demonstrated that single-mode detection can be achieved through the subtraction operation with the reference pixel. The method demonstrated in this study can be applied to any type of uncooled IR sensors to create high-performance wavelength- or polarization-selective absorbers capable of multispectral or polarimetric detection.

**Keywords:** plasmonics; metamaterials; uncooled; IR sensors; wavelength-selective
