Broadband magnetically tunable terahertz isolator based on a metasurface–RIG Faraday rotator

Broadband nonreciprocal components are essential for suppressing unwanted backreflections in terahertz (THz) systems, yet practical THz isolators remain limited by narrow bandwidths, large insertion losses, or strong magnetic-bias requirements. Here, we demonstrate a broadband THz isolator based on an epoxy-engineered metasurface–rare-earth iron garnet magneto-optical element combined with two external linear polarizers. By optimizing the relative polarizer angle to 63°, the broadband Faraday rotation of the metasurface–rare-earth iron garnet structure is converted into strongly asymmetric forward and backward transmission. At room temperature under a magnetic field of 0.22 T, the device exhibits a reliable operating band of 0.40–1.00 THz, corresponding to a continuous bandwidth of 0.60 THz. The band-averaged isolation reaches approximately 30 dB, with a maximum of about 33 dB, while the favored-direction insertion loss remains approximately 5.3 dB. Magnetic field reversal switches the preferred transmission direction, and repeated reassembly measurements confirm stable device performance. These results establish a broadband, magnetically tunable THz isolation platform operating under moderate magnetic bias.