A petrol adulteration sensor based on a rectangular shaped hollow-core photonic crystal fiber is proposed and numerically analyzed in the terahertz regime. The performance of the proposed sensor was evaluated when it is employed to characterize different kerosene mixtures. In this research, the adulterated fuel sample is filled in the rectangular hollow channel and the electromagnetic signal of the terahertz band is also driven through the same channel. The received signal after the interaction of fuel with the terahertz signal will advise the refractive index of the fuel oil inside the core, which will also bear the information of how much extrinsic component is present in the fuel. The finite element method based simulation shows that the proposed sensor can reach a high relative sensitivity of 89% and presents low confinement losses at 2.8 THz. The reported sensing structure is easily realizable with the conventional manufacturing techniques. Consequently, this proposed fiber may be treated as an essential part of real-life applications of petrol adulteration measurements.

In this work, we present a novel scheme to make a controllable, stable, and versatile all-fiber mode converter device. The converter consists of a few modes polarization-maintaining fiber, which is laterally stressed using an electrical actuator. The electrical actuator provides a simple mechanism to control the refractive index changes in the optical fiber thought the elasto-optic phenomena. Thus, it is possible obtain a platform to make mode conversion between the HE11 mode and the TE01, TM01 and HE21 modes. Likewise, the proposed methodology allows controlling the modal conversion trough the variation of the applied force. The results reveal that the performance of the converter depends on the input light polarization, the analyzer angle and the applied force. In addition, the device presents a compact size of 8 cm and shows an excellent performance when is analyzed at 980 nm. Thereby, it is suitable to be implemented for future optical fiber communication systems that employs mode-division multiplexing.