Study On Unidirectional Reflectionlessness Of Silicon Waveguide System Based On Phase Coupling

It is well known that the observable operators in quantum mechanics are Her-mite operators,and their eigenvalues are real.The concept of parity-time(PT)symmetry Hamiltonian was proposed by Bender in 1998.PT symmetry Hamilto-nian describes a new class of non-Hermitian quantum systems,and its eigenvalues can be real if it satisfies PT symmetry conditions.One of the most fascinating features of the PT system is the presence of exceptional points.Beyond this point the real eigen spectrum becomes complex even the PT symmetry is satisfied.The nature of the exceptional points has been discussed in various structures such as metamaterials,optical waveguides,photonic crystals and so on.A photonic crystal is an artificial microstructure material formed by the peri-odic arrangement of mediums.Since its unique photonic bandgap can suppress the spontaneous emission of the material,it can be used as a total reflection mirror,waveguides,optical switches,lasers,detectors and microcavities.Because of the im-portant application prospects of photonic crystals in integrated optoelectronics and quantum optics,the researchers are getting more and more extensive and in-depth research.In this paper,we demonstrate the unidirectional reflectionlessness at exception-al points and non-reciprocal perfect absorption near EPs based on phase coupling between two photonic crystal cavities(PCCs)in optical waveguide.In our scheme,when distance d = 744 nm,the reflectivities for forward and backward directions are closed to～0 and～1,when distance d = 780 nm the reflectivities for backward and forward～0.8 and～0,respectively,and absorptances of the non-reciprocal per-feet absorptions for forward and backward directions are～0.98 and～0.92 with the high quality factors of～1100 and～310,respectively.The structure of this paper provides a good platform for sensors,filters and photonic devices.