Theoretical And Simulation Research On Surface Plasmon Polariton Based Optical Angular Momentum Detectors

Light is an electromagnetic wave that carries information not only about energy but also about momentum.The momentum of light is divided into linear momentum and angular momentum,in which the optical angular momentum includes spin angular momentum and orbital angular momentum.The spin angular momentum is determined by the polarization and can be expressed in two states,left-circular polarization and right-circular polarization.The orbital angular momentum is determined by the spatial phase distribution and can be represented as multiple states which are orthogonal and coaxial.Spin angular momentum and orbital angular momentum not only play a huge role in basic disciplines such as basic physics and quantum optics,but also have huge application potential in interdisciplinary fields such as information communication and biomedicine.Obviously,the applications of spin angular momentum and orbital angular momentum need to be built on the basis of accurate detection.Therefore,it is very important to study the detector of spin angular momentum and orbital angular momentum.There are many methods for detecting the optical angular momentum,such as using wave plates and polarizers to detect spin angular momentum,using interference and diffraction to detect orbital angular momentum.However,these traditional optical angular momentum detection methods have the disadvantages of complicated optical path and large volume,and can only detect single optical angular momentum.In order to optimize the optical angular momentum detection technology,this thesis uses theoretical analysis and numerical simulation to design three optical angular momentum detectors with different functions:First,an x-type angular momentum detector based on surface plasmon polariton is designed.It can detect the linear polarization state and the state between ?1 of orbital angular momentum by etching designed nanoslits array on a 4?m ?4?m gold film.When incident light irradiates the detector,the linear polarization direction of the incident light is first identified according to the coupling direction of the surface plasmon polariton;and then the state between ?1 of orbital angular momentum is detected by calculating the ratio of the light intensity of the exit port to the total intensity of the coupling direction.Then,in order to extend the linear polarization detection to the detection of spin angular momentum,a circular-type angular momentum detector based on surface plasmon polariton is designed.It can detect the ?1 state of spin angular momentum and the ?1 state of orbital angular momentum by etching designed nanoslits array on a 20?m ?20?m silver film.When incident light irradiates the detector,the ?1 state of the spin angular momentum is first identified according to the position where the surface plasmon polariton spot appears;and then the ?1 state of orbital angular momentum is identified based on the shape of the spot.Finally,in order to expand the detection range of orbital angular momentum,a semi-circular-type angular momentum detector based on surface plasmon polariton is designed.It can detect the ?1 state of spin angular momentum and multiple states of orbital angular momentum by etching designed nanoslits array on a 20?m ?20?m gold film.When incident light irradiates the detector,the ?1 state of the spin angular momentum is first identified according to the position where the surface plasmon polariton spot appears;and then the multiple states of the orbital angular momentum are detected based on the position shift of the spot.The traditional optical angular momentum detector can only detect a single optical angular momentum.But the three detectors designed in this thesis can achieve simultaneous detection of spin angular momentum and orbital angular momentum.At the same time,these three optical angular momentum detectors are small in size,simple in structure and accurate in detection.The optical angular momentum detector designed in this thesis can provide new ideas and methods for the detection of optical angular momentum.