The role of Faraday effect on the one-dimensional n-doped Si photonic crystals towards magnetic field sensing applications.

In this study, we have proposed a one-dimensional photonic crystal (1D-PhC) structure for the detection and monitoring of magnetic field intensities. In this regard, the designed magnetic field sensor is introduced to operate in THz frequencies within the wavelength range from 120 μm to 300 μm. The sensing mechanism relies on the Faraday effect, which influences the permittivity of an n-doped silicon that is employed as a defect layer inside the designed PhC structure. Meanwhile, the optimal sensor configuration consists of alternating layers of SiO2 and GaAs, arranged in the form; (SiO2 + GaAs) N=4/ n-doped Si / (SiO2 + GaAs) N=4]. Additionally, the numerical simulations are conducted in the vicinity of the transfer matrix method, plasma model and Faraday effect as well. To improve sensor performance, various structural parameters, including the thickness, doping concentration (Nd) of the n-doped Si layer, the constituent materials of PhC structure, the number of unit cells, and the incident angle as well are optimized. Moreover, the sensor's effectiveness is evaluated based on sensitivity, quality factor (Q-factor), figure of merit (FOM), and detection limit. Upon optimization, the proposed sensor demonstrates a high sensitivity of 2.91 μm/Tesla and a Q-factor of 1600 across a magnetic field range of 1 to 10 Tesla, which proves its ability as a potential magnetic field sensor. Moreover, the designed sensor is robust against structure disorders and geometrical variations as well.