Dual-function plasmonic device on photonic crystal fiber for near to mid-infrared regions

Abstract

Broadband multifunction optical devices can play an important role in the field of integrated photonics but achieving high tunability and versatility on a fabricated device by implementing external control or structural modification is still challenging. In this article, what we believe to be a new dual-function optical device based on photonic crystal fiber, having an ultra-broad bandwidth that partially covers near-infrared (IR) to mid-IR regions, is proposed and analyzed. This device is designed on a fabrication friendly geometry such a way that it can be used as a polarization filter as well as refractive index sensor without any external tuning or structural modification. In this case, plasmonic material plays a crucial role for achieving simultaneous operation of the device both in communication and sensing applications. Our proposed device, with a fiber length of 100 µm, can effectively suppress the y-polarized light within the wavelength range of 1.29 µm to 1.60 µm, while the x-polarized light is maintained properly in the core, and vice-versa for the region of 1.69 µm to 4.39 µm. The maximum confinement losses of 840.8 dB/cm, 1013.2 dB/cm, 659.65 dB/cm, and 792.68 dB/cm are obtained at wavelengths of 1.37 µm, 1.56 µm, 1.72 µm, and 2.65 µm, respectively. By maintaining a crosstalk level of better than 20 dB, this device achieves broad bandwidths of 310 nm over the 1.29 µm to 1.60 µm wavelength range and 2700 nm over the 1.69 µm to 4.39 µm wavelength range. In addition to the filtering performance, our device possesses sensing capabilities, which is also well discussed as an example of refractive index sensor. Considering the analyte refractive index of 1.10-1.40, this device shows an average wavelength sensitivity of 1000 nm/RIU. Therefore, the above exceptional characteristics of our proposed device make it suitable for both optical communication and sensing systems.