Unidirectional Slow Light Transmission in Heterostructure Photonic Crystal Waveguide

Abstract

In conventional photonic crystal systems, extrinsic scattering resulting from random manufacturing defects or environmental changes is a major source of loss that causes performance degradation, and the backscattering loss is amplified as the group velocity slows down. In order to overcome the limitations in slow light systems, we propose a backscattering-immune slow light waveguide design. The waveguide is based on an interface between a square lattice of magneto-optical photonic crystal with precisely tailored rod radii of the first two rows and a titled 45 degrees square lattice of Alumina photonic crystal with an aligned band gap. High group indices of 77, 68, 64, and 60 with the normalized frequency bandwidths of 0.444%, 0.481%, 0.485%, and 0.491% are obtained, respectively. The corresponding normalized delay-bandwidth products remain around 0.32 for all cases, which are higher than previously reported works based on rod radius adjustment. The robustness for the edge modes against different types of interfacial defects is observed for the lack of backward propagation modes at the same frequencies as the unidirectional edge modes. Furthermore, the transmission direction can be controlled by the sign of the externally applied magnetic field normal to the plane.

One-way rotating state of multi-periodicity frequency bands in circular photonic crystal

“…Further calculating, the CPC can also generate one-way rotating state consistent with the one-way resonance mode in the remaining frequencies of each ORMFB. It is proved that CPC can generate one-way rotating state similar to that in the PC based on the other lattices [36][37][38][39][40][41]. The difference is that, the CPC ring resonator designed in this paper can generate eight ORMFBs.…”

“…Among them, the one-way rotating state in PC was found in many structures [36][37][38][39][40][41]. However, the previous works were based on the periodic structure with translational symmetry, such as, square lattice [36][37][38], honeycomb lattice [39,40], or the quasi-periodic structure with rotational symmetry, for example, Penrose-type photonic quasi-crystal [41]. Within a specific frequency range, the one-way rotating state in the periodic structure only exists in two one-way rotating mode frequency bands (ORMFBs) [36][37][38][39][40].…”

“…However, the previous works were based on the periodic structure with translational symmetry, such as, square lattice [36][37][38], honeycomb lattice [39,40], or the quasi-periodic structure with rotational symmetry, for example, Penrose-type photonic quasi-crystal [41]. Within a specific frequency range, the one-way rotating state in the periodic structure only exists in two one-way rotating mode frequency bands (ORMFBs) [36][37][38][39][40]. Both the numbers of the ORMFBs and the total modes are minimal, which lead to the weak adjustability of the obtained one-way rotating state, the relatively weak regularity and the low practicability.…”

Investigating the slow light in a 2D heterostructure photonic crystal composed of circular rods and holes in the square lattices

“…Researchers have therefore managed to enhance the performance of slow light by adjusting the scattering curve of PCW and making changes to the structure [9]. Some of the tuning methods that were proposed previously include changing the radius of the air holes or rods [27,28], shifting the position of the air holes adjacent to linear defects [23,29], microfluidic infiltration [30], and chirped coupled waveguides [22]. Also, various methods are used to create one or more modes in the PC photonic band gap, such as creating a defect in the crystal [31][32][33], using slotted PCW [34], connecting two PCs [35,36], moving the holes in the second row in a triangular lattice, and varying the radius of the holes or rods.…”