Research Of All-fiber Dual-wavelength Acousto-optic Tunable Narrow Band Filters

Optical fiber communication is a particularly important part of modern optical communication system,and its development cannot be separated from all kinds of new optical signal processing devices,among which all optical fiber devices are easy to integrate with optical fiber system,so they play a pivotal role in many devices.In various all-optical devices,the all-optical acousto-optic tunable filter has many advantages,such as wide tuning range,fast tuning speed,low insertion loss,easy preparation and no frequency shift.However,the current light filter is mainly suitable for single wavelength filter,and dual wavelength band pass filter in WDM,microwave photonics and terahertz wave field is very important,it can be used to achieve rapid tuning and narrow bandwidth of the wavelength selector,so the wavelength spacing is far less than 50 nm and efficiency is double wavelength all fiber acousto-optical tunable filter has very important practical significance.In this dissertation,an all-fiber dual-wavelength acousto-optic tunable narrowband filter structure based on vector mode coupling is proposed and fabricated.The research contents are as follows:(1)First of all,through the study of long period fiber grating coupled-mode theory analysis model of acousto-optical Bragg grating coupling process,focus on analysis of fiber core mode and cladding mode coupling process of vector norm,the coupling process polarization rotation in the horizontal electric and magnetic field model,by using the polarization rotation dual wavelength filter characteristics.The relationship between optical fiber parameters and the bandwidth of acousto-optical filter is expounded in detail.(2)Using the finite element analysis software Comsol,to the dispersion compensation fiber modeling,theoretical analysis and calculation model of effective modulus and the effective refractive index,and prove the feasibility of vector mode coupling,and on the basis of analyzing the tuning characteristics,bandwidth characteristics and the characteristics of double wavelength spacing,eventually establish the existing fiber acousto-optic tunable dual wavelength fiber optic parameters of narrow-band filter.(3)An all-fiber dual wavelength acousto-optic tunable narrowband filter was constructed.Through the establishment of experimental platform,the test results show that the filter has realized electric tuning in the range of 1526?1565nm,its 3-d B filter bandwidth is ?1nm,the tuning step length is-0.12nm/k Hz,the insertion loss is 9.4d B,the dual-wavelength spacing is 3.3nm,and it can easily switch the characteristics of band-pass band-reject filter.In the simulation results,the tuning step size of the filter is-0.3nm/k Hz,the dual-wavelength spacing is 3.2nm,and the filter bandwidth is 0.75 nm,which is in the same order of magnitude as the experimental results and basically consistent.(4)Experimental results show that the filter can realize multi-wavelength filtering driven by mixed signals.When different signal frequencies are similar,filter peaks can be overlapped.When the frequency is not close to each other,it can be tuned independently.The all-fiber dual-wavelength acousto-optical tunable narrowband filter proposed in this thesis has many advantages,such as wide range quick tuning,adjustable spacing,low insertion loss,easy preparation,band-pass/band-stop switching,etc.,and can be used in the fields of fast tunable dual-wavelength laser,WDM,micro-photonics and terahertz wave generation.