A compact multi-wavelength isolator using effective epsilon-near-zero and Hall regions

Abstract

Optical isolators play a crucial role in contemporary photonic systems. They ensure unidirectional light transmission and suppress back reflections to stabilize sources. In this study, a compact multi-wavelength Hall-based isolator operating in the mid-infrared (Mid-IR) regime is introduced. It uses the effective epsilon-near-zero (ENZ) and Hall regions of magnetized indium arsenide (InAs) embedded in a photonic crystal. Under transverse magnetic (TM) excitation in the Voigt geometry, this structure breaks time-reversal and mirror symmetries, achieving strong spectral nonreciprocity. The structure supports three distinct isolation wavelengths. One robust isolation point appears in the Hall transparency (HT) region, along with two in the conventional transparency (CT) region. These regions are separated by nearly $4\mu m$, enabling dual-region and multi-wavelength operation. The device also exhibits dual-direction isolation, where different wavelengths prefer opposite transmission directions. Furthermore, the structure naturally functions as a four-port optical circulator. The ENZ-assisted mechanism provides spectral tunability by adjusting the carrier concentration or selecting other ENZ-capable semiconductors. Combining Hall-based operation, high isolation, compactness, tunability, and multi-wavelength behavior, the proposed platform offers a promising solution for next-generation Mid-IR nonreciprocal photonic devices.