Edge State In Magnetic Photonic Crystals And Its Application

Edge state in magnetic photonic crystals (MPCs) has been the hot topic in the past few years. It has been experimentally observed in microwave regime with electromagnetic wave in transverse magnetic (TM) mode transmitting unidirectionally along the edge of MPCs.In general, the formation of one-way edge state is based on two mechanisms, including chiral edge state (CES) which is analogous to quantum Hall effect (QHE) in electron system and the magnetic surface plasmon polariton (SPP). Broken time reversal symmetry is necessary to realize the edge states. The most intriguing property of the edge state is the self-guiding character, which is the electromagnetic wave will go round defects, obstacles and scatters right in the way and keep moving forward. The one-way transport characteristic, immune to backscattering, could be used in nonreciprocal device design and fabrication.Slow wave or slow light could be helpful in next-generation information networks to meet the urgent needs in practical applications, such as a high data rate, high throughput and low power consumption. For the slow wave devices or systems, back scattering is particularly worrisome since it may dominate over all other loss mechanisms as group velocity of waves becomes very small. It will be meaningful for all-optical information processing system which is based on slow light, to introduce into the edge state which is immune to backscatter.Following the predecessors’researches, we studied the characteristics of edge state in MPCs and constructed a slow-wave waveguide basing on it in microwave regime. Main work includes:1. We measured the dispersion relation curves of the edge states in MPCs under two mechanisms with the transplanted phase-shift measurement method. No matter the edge state wave was in waveguide mode or surface wave mode, the measured curves matched well with the simulated band diagram results. This measurement method could be very effective to study on the one-way edge state, especially when it’s hard to calculate the band diagram.2. Basing on electromagnetic CES in MPCs analogous to QHE, we designed and fabricated a unidirectional waveguide. A discussion was made with emphasize on the contributions of two factors, the lattice constant and the distance between metal confinement and MPC, to the one-way waveguide’s working characteristics. Study shows the lattice constant has an evident effect on the unidirectional waveguide’s working frequency. And distance between MPC and metal confinement influences the waveguide’s modes of propagation. Suitable distance leads the waveguide to presenting a better one-way transmission property and less loss. According to simulated results, we fabricated the unidirectional-propagating waveguide and experimentally demonstrated the one-way propagating characteristic which is robust to metal scatters along the waveguide passage in the design regime.3. We measured the dispersion curve of the fabricated one-way waveguide and calculated the group velocity of the edge state transporting along the waveguide passage. The waveguide demonstrated theoretically and experimentally to be a slow-wave one, with group velocity one order of magnitude smaller than the speed of light. The one-way wave with much slower group velocity (approximately0.0005c) was shown in theory by retailoring the waveguide further. The robustness property to backscattering was proved. This waveguide provides a potential way to realize robust slow-light transmission lines in electromagnetic or optical systems.