Research Of A Tunable Filter Based On The SOI Waveguide And Thermo-optic Effect Of The F-P Cavity

As an important device in optical communication networks， tunable filterassumes an very important role in tuning the optical signals, and it is used to select thespecific optical signal which is needed by the user. In order to ensure the highaccuracy，we proposed some details for tunable filters，including the free spectralrange，tunable wavelength range，finesse and so on.Compared with other filters，F-P tunable filter gets better frequency choosingperformance， because the Distributed Bragg Reflector witch F-P tunable filter has cangain a very high reflectivity，and this helps to have a better finesse. Three methodscan be carried out to realize F-P tunable filter：regulating the length of the F-Pcavity， adjusting the angle of the incident light，adjusting the refractive index of theF-P cavity. The thermo-optic effect used in the article choses to adjusting therefractive index of the F-P cavity. We could gradually heating the silicon F-P cavity tochange the transmission light continuously.Because silicon has a large thermo-opticeffect，so we could get a large tunable wavelength.Air layer thickness of390nm, thesilicon layer thickness of110nm, the FP cavity length of8.9μm.The article includes：design main structures of the F-P tunable filter，simulate thecavity heating situation by arranged one by one using ANSYS，design the electrodes，and the design of a digitally controlled power.First， design main structures of the F-P tunable filter， in order to ensurehigh-reflectivity，DBRs should be symmetrical，the difference of different thin-filmdielectric layers’ refractive index should be large，and the film thickness should besticked to the law，so do the F-P cavity，but the size of the F-P cavity should alsoconsider about the material specification of the SOI. Then，a simple structural erroranalysis is taken at the end.Then we use ANSYS to simulate the heating situation of the FP cavity， first wemake a steady-state analysis on the cross-section of the cavity and discuss about someplans about laying the electrodes，after that，we create a3D model and make atransient analysis to obtain the response time of temperature.Rise in response time isabout12μs, decreased response time is about20μs.Then the detail of electrodes is designed based on previous chapter， the purposeof applying electrodes here is to heat the F-P cavity by converting electrical energy into heat， so the most important material specifications are thermal conductivity，specific heat capacity， melting point， resistivity.In order to ensure the filter is continuously adjustable， we make the temperatureto be able to increase slowly， so we have the power obtains a relatively small voltagestep up， we design a digitally controlled power just following this idea. It’s basedwith the atmega8MCU，external the R-2R ladder constitutes a DA converter，whichis used to control the voltage output，also the output terminal coupled with the currentand voltage sampling to ensure the stability of the output， and then the LCD displaycircuit and keyboard circuit complete the entire power. Programs on the MCU， ismade up of the power-on initialization，interrupt and loop. It is considered that thispower could output0~10V and make the F-P filter a0.05nm stepping up by stepping...