Study On Optical Transmission And Its Nonlinear Effects In Non-hermitian Cavity Optomechanical System

In recent years,non-Hermitian physics research on PT(Parity-Time)-symmetry has witnessed vigorous development in optics and photonics.PT-symmetric system has a non-Hermitian-Hamiltonian quantity,which can show the spontaneous transition from the PT-symmetric phase to the PT-broken phase,and is accompanied by the change of the eigenvalue of the system from real to complex.In particular,the critical points at which PT-symmetry is broken are called EPs(exceptional points).PT-symmetric optical structure constructed through gain-loss balance can utilize the coupling effect between gain,loss and optical devices to control optical transmission characteristics and nonlinear effects.The optical system constructed by combining PT-symmetry has achieved a lot of important research results in light wave transmission and laser theory.Among them,EPs effect has important research in single-mode laser preparation,optical signal non-reciprocal transmission and quantum sensing.On the other hand,based on the rapid development of micro-cavity structure,cavity optomechanics has become an important platform for exploring the interaction between light and matter,and some landmark results have been achieved,such as ground state cooling,optomechanically induced transparency,entangled state preparation,etc.It has important application value in basic physics and quantum information process.Therefore,extending PT-symmetry to cavity optomechanics has become an important research direction.In this paper,based on optomechanical nonlinear interaction,three non-Hermitian cavity optomechanical structures are constructed to systematically study the influence of PT-symmetry and EPs effect on the optical transmission characteristics and nonlinear effects in the cavity optomechanical system.The main research contents of the thesis are as follows:1.We use the flexibility of thin-film oscillators to achieve double-phonon induced transparency in the PT-symmetric optomechanical system.On the basis of the cavity optomechanical system,the introduction of an auxiliary gain cavity can successfully construct a cavity optomechanical system that satisfies the PT-symmetry.Through numerical calculation,the output spectrum of the probe field can produce optomechanically induced transparency,which essentially takes advantage of the spontaneous breaking of PT-symmetry and enhances the quadratic optomechanical coupling.When the PT-symmetry is maintained,the eigenmode of the system splits to form two supermodes;optomechanically induced transparency can be converted between the two supermodes by selecting appropriate parameters.In addition,the temperature parameter can regulate the intensity of optomechanically induced transparency.These results have potential application value in the transmission,storage and conversion of optical signals.2.We propose a new scheme to enhance optomechanically induced sum sidesband effect through EPs in the mechanical PT-symmetric system.Sum sidesband can realized in a double-probe-field-driven optomechanical systems and considering the inherent nonlinearity of the optomechanical coupling,but the efficiency of the sum sideband is very low.The non-Hermitian cavity optomechanical system constructed by the PT-symmetric mechanical resonator can produce the EPs effect.Due to its unique characteristics,the EPs effect has been used to prepare phonon laser and non-reciprocal transmission of optical signals.In the vicinity of EPs,the efficiency of the sum sideband can be significantly enhanced,even by three orders of magnitude;and the sum sideband effect can be applied to the optical signal modulation on-chip optical communications.This research provides a new idea,that is,through the combination of EPs and optical nonlinearity,it can be used to enhance the optomechanical nonlinearity research in the cavity optomechanical system.3.We discuss that the EPs effect can enhance optomechanically induced high-order sideband generation in a dissipatively coupled whispering-gallery-mode microresonator.The high-order sideband effect is generated under the condition of considering the inherent nonlinearity of the optomechanical coupling.Because of the weak coupling mechanism,its formation efficiency is relatively low.Because of its important applications in the exploration of quantum nonlinear effects and high-precision measurement,it has been widely studied.When the optical field drives the whispering-gallery-mode microresonator that couples two nanoparticles,two opposing optical modes are generated in the non-Hermitian optomechanical system we constructed.And,the dissipative coupling of the two optical modes occurs near the nanoparticles.EPs effect can be achieved by modulating the phase between two nanoparticles.On the one hand,in the vicinity of EPs,the efficiency of second-order sideband generation can be significantly enhanced.Meanwhile,based on the highly sensitive response of EPs to perturbations,we can realise the effective conversion between optomechanically induced transparency and second-order sideband;On the other hand,in the non-perturbation regime,the high-order sideband effect can be enhanced by changing the driving power of the probe field in the EPs.This greatly enriches the research of optomechanically nonlinearity.