The Broken Condition And Regulation Of PT Symmetric Waveguide System

The concept of parity-time symmetry(PT symmetry)improves the theory of traditional quantum mechanics in the non-Hermitian range.It requires that the real part of potential function of Hamiltonian is even and the imaginary part is odd.Then PT symmetry is introduced into the optical field.Combined with mature optoelectronic technology,PT symmetry system can be easily constructed based on gain and loss media.However,under the actual experimental conditions,it is difficult to fabricate a PT symmetric system which has a complete conjugated symmetric complex refractive index.Therefore,based on PT symmetric waveguide system and the theory of coupled mode,an analytic method suitable for general PT symmetric waveguide system is proposed in this paper.The broken condition of the system is analyzed numerically.And a method to regulate the broken condition is proposed.At last,several non-reciprocal PT symmetric optical waveguide devices are designed.The main contents of this paper are as follows:1.The general PT symmetric waveguide system is theoretically analyzed.We apply the coupled-mode theory,which is applicable to the complex refractive index medium,to the analysis of general PT symmetric waveguide systems.The broken condition of PT symmetric waveguide system can be deduced accurately by this method.Then taking conjugated and non-conjugated PT symmetric waveguide system as examples,the broken condition is analyzed,and the expressions of broken point in these two cases are derived.Finally,the results are verified by FDTD simulation.2.Based on the coupled-mode theory with complex refractive index,the broken condition of PT symmetric waveguide system is analyzed.And a method to regulate the broken condition of PT symmetric waveguide system is proposed.For a given waveguide material,it is convenient to regulate the broken condition of a waveguide system by properly designing the size of the waveguide.3.Three kinds of nonreciprocal PT symmetric optical waveguide devices,including PT symletric non-reciprocal polarization beam splitter,non-parallel PT symetric directional coupler and PT symmetric tapered waveguide,are numerically analyzed and designed.These devices are simulated by FDTD software to verify the non-reciprocal transmission characteristic.Based on the method of regulating broken condition,the spontaneous breakage is realized in the non-parallel PT symmetric directional coupler and the PT symmetric tapered waveguide.Finally,the layout of basic optical waveguide devices is designed and preliminary experimental exploration is carried out.