Research On Silicon-based Mach-Zehnder Modulator Based On Thermo-optic Effect

In recent decades,silicon photonics devices in the near-infrared have been well developed due to their important applications in the field of communication.However,the research of silicon photonics in the mid-infrared(2.5-25 ?m).still needs to be explored.The silicon-based integrated photonic devices in the mid-infrared can be widely used in waveguide,light source,modulator,detector,spectrometer,etc.,among which the micro-integrated spectrometers have attracted a wide range of interest,and opened applications in chemical medicine,biosensing and environmental monitoring and other related fields.Compare with traditional spectrometer,the Fourier transform infrared spectrometer(FTIR)has the advantages of high spectral resolution,wide spectral range and short measuring time.However,the traditional Michelson interferometer as its core component still has the disadvantages of high optical loss and low stability.Therefore,a new type of thermal modulated interferometer which can be applied to the micro Fourier transform infrared spectrometer has become the focus in recent research.In this project a silicon waveguide-based Mach-Zehnder interferometer(MZI)modulator was designed based on thermo-optic effect.By integrating a metal heater with the signal arm of the MZI waveguide,the waveguide refractive index is modulated by joule heat and the output light can be effectively controlled.In this project a simulation model for the design of such a thermo-optic modulator was firstly built.The dimensions of the MZI and the heater are optimized to obtain a relatively good performance characteristic by minimizing transmission loss and reducing electric power dissipation.According to the simulation model,the theoretical propagation losses of 1.6 dB/cm and the switching power of 40.80 mW per heater is calculated.On this basis,we combine the designed MZI structure with other passive components in the silicon-on-insulator(SOI)material platform and the on-chip thermo-optic modulator is fabricated and characteristic in lab.According to the experimental results,at the operating wavelength of 3.8 ?m,the SOI waveguide is demonstrated with propagation losses around 8.430 dB/cm.The MZI modulator is measured to have insertion losses about 0.378 dB and the extinction ratio of 25.4 dB.The low modulation power of 35.2 mW is achieved.The thermal modulator can be used as the core component of micro-integrated mid-infrared spectrometer,which not only greatly reduces the footprint of device and the power consumption of modulator,but also improves the system stability.This work has laid a foundation for the realization of on-chip silicon spectrometer in the mid-infrared.