Research On Bending Loss And Miniaturization Of Optical Nonreciprocal Transmission System Of Tapered Optical Fiber

As a perfect combination of nanotechnology and fiber optics,tapered optical fiber has been widely studied and applied in the fields of light generation,transmission,regulation,conversion and measurement in recent years.Tapered optical fiber not only has the advantages of low transmission loss and controllable preparation process like traditional fiber,but also has new characteristics such as strong light field constraint ability and high evanescent field proportion because the working area diameter is close to the wavelength of transmitted light and large difference of refractive index of the cladding and core.Therefore,tapered optical fibers have outstanding applications in optical sensors and optical non-reciprocal transmission systems,which respectively take advantage of the power loss of fiber after bending by external forces and the strong evanescent field in the waist region.This paper exactly pays close attention to these two aspects.Firstly,we use the finite element method to study the bending loss and deformation under stress of the whole adiabatic linearly tapered optical fiber under different bending radius at each position.It is found that the core mode cutoff region in the tapered transition region of the fiber is particularly sensitive to the bending,because the adiabatic condition at this position is most easily destroyed.In addition,the transmittance of fiber increases first and then decreases abnormally under small bending radius in this region.These results can provide great reference value for the fabrication of tapered optical fiber pressure sensor and other sensing applications.On the other hand,an experimental scheme and device for realizing optical non-reciprocal transmission based on the interaction between tapered optical fiber and warm rubidium atoms are proposed,and a miniaturized interacting system is built.The system is small in volume and can be independent of the vacuum system and portable,which is an important step for realizing the miniaturization and integration of non-magnetic optical non-reciprocal devices.