Study On Unidirectional Transmission Based On Self-Collimation Effect In Photonic Crystal

With the increasing difficulty of the process,the integration of integrated circuits(IC)approaches the limit.In addition,electronic devices consume significant amount of energy and generate a large amount of heat in the information processing and computing,due to the intrinsic properties of electrons and electrical resistance.Therefore,it is desired to seek new information processing and computing technologies to overcome those bottleneck issues.Compared to election,photon can efficiently propagate in optical waveguides and be used in quantum computing with high efficiency and without heat generation.Thus,photon is a promising candidate in the next generation of information processing and quantum computing technologies.Therefore,it is important to build a platform with photonic devices with different functionalities to enable the all optical communication and quantum computing.Similar to electronic diodes,the optical unidirectional transmission devices are important building block in integrated photonic circuits.The unidirectional transmission devices for photons diodes are useful in integrated photonic systems because it can perform logic operations.At present,micro-nanoscale photonic diodes based on spatial inversion asymmetry are limited by material loss,bandgap width and band matching,and have low forward transmittance,low contrast ratio,narrow bandwidth and only work for a specific polarization state.In order to design all-optical diodes with high forward transmittance,wide wavelength range,suitable for any polarization state and easy integration,we design a two-dimensional photonic crystal(Ph C)heterostructure based on the self-collimating effect and bandgap properties,which is composed of two square lattice photonic crystals Ph C1 and Ph C2 with different lattice constants and lattice shape.This method breaks the current bottleneck in the research of integrated micro-nanoscale photonic diodes and lays a solid foundation for the design and manufacture of highly integrated optical quantum chips.The main work are as follows:1.Selecting integrable material silicon to design heterogeneous photonic crystals,we use theoretical analysis and numerical methods to calculate energy band structure,equal-frequency contour and electric field distribution,illustrating self-collimation effect mechanism;It is to reveal the role of self-collimation effect of photonic crystal structures in improving the forward transmittance of the light wave,through analysis of photonic crystals with different structures.It is to optimize the lattice structure parameters and finally achieve a high forward transmittance and high contrast ratio of unidirectional transmission of arbitrary polarization states in a broad wavelength range.This strategy provides a new way for implementing integrated photonic diodes and has scientific value and practical significance.2.Here we demonstrate a photonic crystal heterostructure with elliptical shape lattice with 2-fold rotational symmetry for highly efficient unidirectional transmission of light based on the self-collimation effect.The forward transmitted light can be collimated along the propagation direction and efficiently coupled out of the structure.Thus,high forward transmittance up to 0.661 and 0.581 for TE and TM polarized modes can be achieved by this design at the telecommunication wavelength of 1550 nm,respectively.Unidirectional transmittance bandwidth with forward transmittance more than 0.5 reached 561 nm and 451 nm for TE and TM polarized modes.The 2-fold rotational symmetry allows further optimizing the structure by tuning the angle between the major axis of the ellipse and the ?-X direction,and found that high forward transmittance can be achieved when the major axis of the ellipse is along ?-X direction.In addition,the design shows weak polarization dependence,thus it works for both TE and TM polarization states with high performance.Therefore,the elliptical photonic crystal heterostructure lays the foundation for high performance unidirectional transmission devices.Because the structure is made of silicon material,it is convenient for experimental preparation.This design principle can be further applied to other photonic devices.3.This structure uses silicon material to construct a square lattice.Using self-collimating of square air hole photonic crystal the forward incident light from different incident angle to couple to the output waveguide,we are able to significantly increase the forward transmittance for both TE and TM polarized light to >0.5.By calculating the transmittance and contrast ratio spectra,it shows that the forward transmittance and contrast ratio are 0.693 and 0.946 at the optical communication wavelength of 1550 nm for TE polarized light.On the other hand,for TM polarized light,the forward transmittance and contrast ratio are 0.513 and 0.972,respectively,at 1550 nm wavelength.Thus,it is confirmed that the Ph C heterostructure achieves highly efficient,broadband and polarization independent unidirectional transmission.Finally,to further improve the forward transmittance of the TE polarized light,we modulate the radius of the front row of photonics lattice of Ph C1 at the interface.It shows that the forward transmittance can be further improve to a record high value of 0.832 for TE polarized light.Our design opens up new possibility in designing photonic diodes based on Ph C and will find broad applications as the design can be fabricated by current nanofabrication techniques.