Research Of Silicon-based WDM Devices

With the development of the Internet era,a wealth of telecommunication services have been derived,which challenges the existing communication capacity.In order to meet the demand and development trend of larger information capacity and faster transmission rate,a new generation of ultra-high speed optical fiber transmission technology is proposed:Wavelength Division Multiplexing?WDM?.Multiplexers/demultiplexers are the core devices of WDM,which have important research significance.In this paper,based on planar waveguide,several WDM devices are designed.?1?A polarization-sensitive triplexer based on multimode interference?MMI?is proposed.According to the principle of MMI,the beat lengths vary with working wavelengths.Using the structure of tilted MMI waveguide,by choosing the position and tilt angle of the output waveguide reasonably,each wavelength can be output from different image points to achieve wavelength separation.The results show that the length of the MMI waveguide is only 150?m,the normalized output power of 1550 nm,1490 nm and 1310 nm is-0.97 d B,-1.55 d B and-1.49 d B,respectively.?2?An ultra-compact 1×2 demultiplexer based on MMI waveguide is proposed to separate the1310 nm and 1550 nm wavelengths,which uses Si₃N₄/SiN_x/Si₃N₄sandwiched structure to realize polarization insensitivity.The beat lengths for the two orthogonal polarization states at same wavelength can be identical by choosing the proper refractive index of the SiN_x,whereby polarization insensitivity is realized.By choosing the proper length and width of MMI,a single image and a mirror image for the two working wavelengths are formed respectively,whereby the two wavelengths are successfully separated.The results show that the size of the MMI waveguide is 4.6×227.7?m²;the insertion losses and crosstalk are as low as 0.18 d B and-25.7 d B respectively;and the broad 3 d B bandwidth of 60 nm is achieved.?3?An ultra-compact 1×2 demultiplexer based on directional coupler?DC?waveguide is proposed to separate the 1310 nm and 1550 nm wavelengths,which uses Si₃N₄/SiN_x/Si₃N₄sandwiched structure to realize polarization insensitivity.The coupling lengths for the two orthogonal polarization states at same wavelength can be identical by choosing the proper gap between two parallel SiN_x waveguides,whereby polarization insensitivity is realized.Two working wavelengths will output from different output ports by choosing the proper width of sandwiched waveguide,whereby the two wavelengths are successfully separated.The results show that the length of the DC waveguide is only 23?m;the insertion losses and crosstalk are as low as 0.1 d B and-26.23 d B respectively;and the 3 d B bandwidth of 200 nm is achieved.In summary,three devices are designed in this paper,the former uses a single MMI waveguide,which greatly shortens the length of the device;the latter two are based on Si₃N₄/SiO₂ platform,which can effectively reduce the size of the waveguide,improve the integration,reduce the loss and realize polarization-insensitive.These devices have potential application value in the future integrated optical circuit.