This paper presents a novel magneto-optical isolator based on an ultra-wideband and high efficiency photonic crystals (PCs) waveguide and gyromagnetic ferrites. The three-dimensional numerical simulation finds that the photonic crystals waveguide’s (PCW) transmission efficiency rises with its height and width. The corresponding experiments are performed by using a triangular lattice Al₂O₃ dielectric posts array in 5G millimeter wave band. The measured transmission efficiency is up to 90.78% for the optimal PCs waveguide structure, which has ultra-wide operating bandwidth from 23.45 to 31.25 GHz. The magneto-optical isolator is designed by inserting two rectangular gyromagnetic ferrites into the PCs waveguide. Due to the contrast between the effective permeability of the left and right circular polarization waves passing through the magnetized ferrite sheets, the ferromagnetic resonance absorption of the forward and reverse waves is different. By using finite element method, the isolation is optimized to be 49.49 dB for the isolator and its relative bandwidth reaches 8.85%. The high isolation, broadband, and easy integration indicate that our designed magneto-optical isolator has significant advantage in 5G communication systems.

In this paper, a terahertz circulator based on a magneto photonic crystal slab is envisaged. The triangular lattice photonic crystals with a line defect waveguide were constructed on an Al₂O₃ ceramic slab. Two cylindrical ferrites and two copper-clad plates in the junction of the Y-shaped wave-guide worked as a magneto-optical cavity resonator to approve the nonreciprocal function. In the working frequency range, 0.212–0.238 THz, the isolation of the circulator was better than 20 dB, and the insertion loss was better than 1 dB. The designed circulator based on the magneto photonic crystal slab experienced low loss and a wide bandwidth that satisfied its use in the THz application.

This paper presents a novel four ports double Y-shaped photonic crystals circulator with ultra-wide bandwidth in 5G millimeter wave band. Its insertion loss can be designed as low as 0.38 dB at 26.10 GHz while its optimal isolation is up to 74.86 dB at 25.00 GHz. The circulator keeps its isolation above 20 dB from 21.80 to 29.04 GHz. Our simulations also show the relative bandwidth can be effectively broadened to be 28.48% through adding an impedance matching transformer composed of four triangular metal pedestals. We confirmed our theoretical results with a circulator sample made of a triangular-lattice Al ₂ O ₃ ceramic rod array and ferrite posts. The minimal measured isolation and insertion loss have reach 47.61 dB and 0.80 dB at 25.55 GHz and 26.10 GHz, respectively. The operating spectral region of our sample covers from 24.08 to 28.23 GHz (the relative bandwidth is 15.87%), which is about seven times higher than the best simulated result of 2.5% and fifteen times higher than 1.07%, the published experimental value. Our experimental results are well matched with the numerical simulations. The low loss, high isolation and ultra-wideband characteristics demonstrate that our photonic crystal circulator has potential applications in 5G communication systems.