Study On The Multimode Grating Filter Based On Silicon

As one of the most important devices in optics,the Bragg grating has been widely used in lasers,Wavelength-Division Multiplexing(WDM),sensor,dispersion compensation and other fields.With the rapid development of silicon-based photonics,scholars have deeply studied the silicon grating filters.As the fabrication process based on SOI(Silicon-on-insulator,SOI)is simple,compatible with the CMOS process,convenient for large-scale production,the waveguide grating has become one of the most important devices in silicon-based integrated photonics.Silicon-based multimode waveguide grating,one of the Bragg gratings,has attract lots of attention,due to its large tolerance,multiplex and modes conversion.Therefore,further research on silicon-based multimode waveguide grating and designing novel functional devices based on multi-mode waveguide grating is of great significance.In this dissertation,several filters based on multimode waveguide gratings are proposed.The main innovations and work lie below:1.A new low loss band-pass and band-rejection grating filter is proposed.By combing the asymmetric multimode waveguide grating and the adiabatic coupler,a low loss band-pass band-rejection grating filter is achieved,while eliminating negative parts and increasing steability.The experiment measured insertion loss is only about 0.6 dB.Then an on-chip add-drop filter is designed,while a phase-shifting grating filter with ultra-narrow band-pass was achieved on this basis.2.A lateral-apodized multimode waveguide grating filter is proposed.By adjusting the relative position of the grating teeth on both sides of the stripe multimode waveguide grating,the sidelobe of the silicon based waveguide grating filter is suppressed.Theoretically,the sidelobe suppression ability with different bandwidth and different coefficients is demonstrated.And it was verified experimentally,with the extinction ratio of the drop signal is more than 18 dB.The lateral-apodized structure overcomes the problem of single side sidelobe suppression of grating with amplitude apodization.At the same time,it possesses the advantages of simple fabrication and large tolerance.3.An ulatra-broadband bandwidth tunable filter with large tunable range is proposed.It is composed of two cascaded asymmetrical multimode waveguide gratings,while the tunable-bandwidth functions of drop/through ports are achieved.Compared with other structures based on cascaded gratings,the structure avoids the waste of energy.The experiment result shows that the filter bandwidth can be continuously tuned in the range of 117GHz-1.572 THz by adjusting the resonant wavelength of two grating filters.Compared with other tunable filters based on micro ring and MMI,this structure has no FSR limitation with large tunable range,which is of great significance for the achievement of reconfigurable on-chip optical network.