带空气狭缝倒置结构的脊型硫系光波导后向受激布里渊散射研究

Study on backward stimulated Brillouin scattering of chalcogenide inverted-ridge optical waveguide with air slot

受激布里渊散射效应具有光谱线宽窄、频率稳定和增益方向敏感等优点,常用于激光器,慢光产生和微波光子滤波器等.本文基于As_(2)S_(3)硫系玻璃、以SiO_(2)为衬底设计了一种亚微米尺寸的带空气狭缝倒置结构脊型波导结构,具有高达8.22×10^(4)W^(–1)·m^(–1)的后向受激布里渊散射增益系数.研究显示在该结构的同种光学和声学模式下,更小的声光场有效模场面积具有更高的后向受激布里渊散射增益系数.还分析了硫系玻璃的光学损耗对后向受激布里渊散射的影响,发现当波导长度超过最优值后,斯托克斯光波功率开始下降,而增大泵浦光功率不仅可以提高斯托克斯光波功率的极大值,同时还会增大波导长度的最优值.当所输入的泵浦光功率为20 mW时,受激布里渊散射增益达到100 d B波导长度仅需要2 cm,这非常有利于光子器件的片上集成.

The stimulated Brillouin scattering(SBS) effect has the advantages of narrow spectral line width,frequency stability,and sensitivity to gain direction,which is commonly used in the field of integrated photonic devices,such as lasers,slow light generation and microwave photonic filters.In practical applications,due to the low gain coefficient of SBS in traditional chalcogenide waveguides,there are high threshold of pumping power and long waveguide length.In this work,an inverted-ridge waveguide structure with air slot is designed by adopting As_2S_(3) and SiO_2,which presents high backward stimulated Brillouin scattering(BSBS) gain coefficient.This chalcogenide inverted-ridge optical waveguide with air slot can better confine the optical field and acoustic field within the ridge region for improving the coupling efficiency between optical field and acoustic field.More significantly,adding an air slot into the ridge region of this chalcogenide waveguide will produce powerful radiation pressure at the boundary between the air slot and As_2S_3.Owing to the fact that the acoustic field is mainly distributed near the air slot in the ridge region,the coupling effect of the radiation pressure and acoustic field is significantly enhanced,leading to a significant increase in BSBS gain coefficient.In this work,the optical fundamental mode as optical mode due to the chalcogenide waveguide with submicron size structure and the six lowest order acoustic modes that meet the matching vector conditions as acoustic mode are calculated,and it is found that the fifth order acoustic mode achieves a maximum BSBS gain coefficient in the six acoustic modes.On this basis,by scanning the waveguide structural parameters of the air slot width,waveguide ridge width and height,and waveguide thickness,the BSBS gain coefficient is as high as 8.22×10~4 W~(–1)·m~(–1),which is more than three times the currently reported chalcogenide waveguide with nonsuspended structure.Additionally,the calculation results also indicate that this chalcogenide waveguide with a smaller effective mode field area has a higher BSBS gain coefficient in the same optical mode and acoustic mode,providing a new idea for further improving the BSBS gain coefficient in the design of waveguide structure.At the same time,the influence of optical loss on BSBS gain is also analyzed,and it is found that when the waveguide length exceeds the optimal value,the lost energy caused by the optical loss will be beyond the input energy of the pump optical wave,causing the power of the stokes optical wave to begin to decrease.However,the improvement of the power of pump optical wave not only increases the maximum power of the Stokes optical wave,but also raises the optimal value of the waveguide length.The results of simulation calculation show that when the input power of pump optical wave is about 20 mW,this chalcogenide waveguide with only 2 cm waveguide length has a BSBS gain of 100 dB,which has the advantages of low pumping power and short waveguide length in the currently reported on-chip integration of chalcogenide waveguides.