| Fiber Bragg grating is a special optical intermode interference fiber device widely used in the field of modern sensing and communication.Because of its antielectromagnetic interference,corrosion resistance,small size,lightweight,high sensitivity and low cost,it has attracted widespread attention in recent years.In addition to the characteristics of narrow band filtering,the large proportion of evanescent field also makes the etching Bragg grating on micro-nano fiber have a high sensitivity response to the change of environmental parameters.In this paper,two kinds of large-scale tunable optical devices based on micro-nano fiber Bragg grating structure are studied,and their tuning characteristics are deeply explored.The main contents of this paper are as follows:1)The relevant background and research status of micro-nano fiber Bragg grating are introduced in detail,the preparation process of micro-nano fiber Bragg grating is elaborated,and the coupling mode theory of micro-nano fiber Bragg grating is analyzed theoretically,and the electric field distribution of micro-nano fiber Bragg grating is simulated by finite primitive method.2)A micro-nano fiber Bragg grating magneto-optical tunable filter based on magnetic fluid coating is proposed and implemented.The simulation results show that the tuning sensitivity and range of the system are negatively correlated with the diameter of micro-nano fiber.Considering the attenuation of reflection spectrum,a micro-nano fiber with a diameter of 9.24 um is prepared on the basis of theoretical calculation.The maximum tuning sensitivity of the filter is 36.2pm/m T and the tuning range is 1.94 nm in the field intensity range of 0-160 m T.It has a good application prospect in modulation of weak magnetic field,geological environment monitoring and chemical microdetection.3)A micro-nano fiber Bragg grating all-optical tunable filter based on ultra-thin liquid crystal coating is proposed and implemented.The reorientation of liquid crystal molecules induced by 0.5m W/mm2 Ar+ laser induced by nematic liquid crystal doped with methyl red sodium salt dye material leads to the high refractive effect of liquid crystal coating and the shift of the wavelength of the reflection spectrum of micro/nano fiber Bragg grating.The refractive index around a specific liquid crystal coating can be adjusted for optimal performance by changing the thickness of the coating and the diameter of the micro/nano fiber.This optimization results in a larger tuning range,lower insertion loss,and a higher extinction ratio.The maximum wavelength shift of the experiment was 1.32 nm.It can be used as an active filter or optical fiber sensing device. |
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