Research On All-optical Tunable Microfiber Knot Resonator With Graphene-assisted

Microfiber knot resonator has attracted wide attention in the field of optical communication and optical information processing due to its unique wavelength selection characteristics and excellent resonant enhanced characteristics.Because of its low cost,stable structure,simple fabrication process and easy integration of optical devices,microfiber knot resonators have been widely applied as optical filters,optical modulators,optical sensors and other devices.With the demand for high-speed and large bandwidth,the use of all optical communication to achieve modulation and detection of optical signals has become a hot topic in the field of scientific research.The tunable characteristics of devices are the basis of all optical modulation.Therefore,the research on tunable characteristics of microfiber knot resonators is highly appreciated.The essence of all-optical tuning is light-control-light.The use of optical nonlinear effects to realize light-control-light has become a hot topic.However,the traditional standard optical fiber nonlinearity coefficient is very low.This fatal disadvantage greatly hinders the possibility of effective all-optical tuning of microfiber knot resonator.In order to improve the nonlinear coefficient of optical fiber,the method of adding high nonlinear materials in the traditional optical fiber has been proposed,but its nonlinear coefficient is still very low.The other way to increase fiber nonlinear coefficient is proposed,which is used two-dimensional graphene materials to coating on the surface of microfiber to improve the nonlinear coefficient of the fiber by enhancing the interaction between light and graphene.Graphene is a new type of two-dimensional material with thickness of single atomic layer.Because of its outstanding stability,unique energy band structure,simple preparation method and excellent optical properties,graphene is hot in research field.As the basis for the study of the interaction between light and matter,a microfiber with low loss and strong evanescent field can be produced by using the flame drawing taper technology.Through the ingenious combination of graphene and microfibers,the interaction between light and graphene can be enhanced significantly.It provides a new idea for the research of all optical tunable devices based on microfiber.Based on the above,we propose a new structure of graphene assisted all optical tunable microfiber knot resonator,which lays a solid foundation for the research of high-speed all-optical modulation with micro cavity fiber resonator.Direct interaction between light and graphene is achieved by irradiation of the external pump light.By using the thermal optic effect and optical nonlinear effect of graphene,the effective tuning of the transmission loss,extinction ratio and resonant wavelength of the microfiber knot resonator is realized.The tuning efficiency of the transmission loss is increased by 69 times,and the tuning efficiency of the extinction ratio is increased by 125 times.The tuning range of the resonant wavelength can cover the transparent window of the entire wavelength of the fiber used.