Research On Tamm States In One-dimensional Mirror-symmetric Photonic Crystals

With the progress of the times and the development of science and technology,the level of communication technology has also been increasing.With natural materials and structures gradually failing to meet the technical requirements,photonic crystals,as a new type of artificial micro and nano-level optical material,have received increasing attention in electromagnetic wave control,microwave antennas,electromagnetic protection and optical fiber fabrication due to their special optical properties and explorability.In this paper,the electromagnetic propagation characteristics of multi-interface Tamm states are theoretically analysed and investigated using the transmission matrix method based on the construction of a one-dimensional mirror-symmetric composite photonic crystal structure containing defects.The energy band diagrams of the structure as well as the transmission spectrograms are analysed by transmission and reflection coefficients,and the effects of the location of the defects,size,magneto-optical material and gain/loss factor on the transmission characteristics of the photonic crystal are studied,mainly as follows:(1)A one-dimensional mirror symmetric photonic crystal structure is constructed.The propagation characteristics of one-dimensional mirror symmetric photonic crystals are studied using the transmission matrix method.And then,the conditions of optical Tamm state excitation at the interface of the symmetry axis are studied.And based on the one-dimensional mirrorsymmetric composite photonic crystal structure,a central defect layer is introduced at the position of the symmetry axis of the model to derive the conditions of the optical Tamm state when the defect layer is contained.The propagation characteristics of the model are analysed according to the energy band diagram and transmission spectrogram,and the effect of the thickness of the central defect layer on the frequency of the transmission peak of the optical Tamm state is investigated,with the increase of the thickness of the central defect layer,the transmission peak of the optical Tamm state moves towards the lower frequency.On this basis,the multimode phenomenon in the forbidden band range and its laws are investigated when a certain thickness of defect layer is introduced at the interface.When the thickness of the central defect layer satisfies the optical Tamm state dispersion relation containing the defect,more optical Tamm state resonance transmission peaks are excited in the forbidden band.(2)The one-dimensional mirror-symmetric photonic crystal structure with symmetric defect layers is constructed,and the effect of symmetric defects on propagation characteristics is analyzed and researched.The results show that as the incidence angle increases,the dispersion curves of the Tamm state in the bandgap move to a high frequency.When the thickness of the symmetrical defect layer increases,the transmission peak evolves from the high-frequency of the band gap to the low-frequency direction.When the position of the symmetric defect layer is far from the intermediate interface,the transmission peaks on both sides approach the Tamm state of the intermediate interface and finally merge into a Tamm state of the intermediate interface.It is further analyzed that the cause of introducing a new transmission peak of the symmetric defect layer is that the defect truncates the original periodic structure of the composite photonic crystal,and new optical Tamm states are generated at the defect truncation interface.On this basis,the multi-mode phenomena and properties in the gap range are compared when the thickness of the central defect layer and the symmetric defect layer increases.When the thickness of the symmetric defect layer satisfies the optical Tamm state condition with defects,multiple optical Tamm state resonance transmission peaks will also be excited in the band gap.(3)The propagation characteristics of nonreciprocal Tamm states in a one-dimensional mirror symmetric magneto-optical photonic crystals with symmetric defect layers are investigated.The influence of the Angle of incidence,the thickness of the symmetric defect layer and the position of the symmetric defect layer on the strength of the nonreciprocity of the Tamm state are studied and analyzed.The results show that the Tamm state located at the centre of the energy gap has stronger nonreciprocity than the Tamm state situated at the edge of the energy gap.As the incidence Angle increases,the nonreciprocity of the multimode Tamm state gradually increases.When the thickness and position of the symmetric defect layer change,the frequency of the multimode Tamm state changes accordingly to change the relative position of the transmission peak of the Tamm state in the gap band,but it has little effect on the strength of the nonreciprocity of the Tamm state.(4)The study of anomalous transmission in a model of a one-dimensional mirror-symmetric magneto-optical photonic crystal structure after the introduction of a gain-loss factor.When the magnitude of the gain/loss factor in the structure is large enough to break the PT symmetry of the structure,anomalous transmission of the model is excited.The creation of spatial symmetry breaking by varying the thickness of the unilateral defect layer and the magnitude of the unilateral applied static magnetic field,respectively,to break the PT symmetry of the structure and excite anomalous transmission of the model at a small gain/loss factor is investigated.