Study On The Filters Based On Waveguide Gratings For The DWDM System

As one of the most important roles in integrated optical communication,optical sensing,and optical interconnect,silicon photonics has been the hot area of research in domestic and overseas.As one important part of silicon optical devices,grating can be applied in wavelength-division-multiplexing devices,polarization isolators,mode isolators,and splitters.Bragg grating is a kind of gratings,which has the merits of unlimited FSR and can be applied in many filters.However,it is hard for Bragg grating to be used in the DWDM system since it has a large bandwidth.In this paper,a multi-channel DWDM tunable add/drop demultiplexer based on silicon waveguide Bragg gratings is demonstrated,and proved to be practical through the experiment measurements.The main novelty and work include the following aspects:1.A novel filer is demonstrated using a phase-modulated apodization method based on the previous work in view of the sidelobes of the uniform grating.Grating-assisted couplers with the grating teeth featuring constant depth and variable location are applied in the method.Firstly,the implementation principle is analyzed.Then,the comparative simulation between apodized gratings and uniform gratings is done based on the simulation software.At last,the measurement results show that a sidelobe-suppression ratio larger than 20 dB is obtained.2.A method of cascading is used to modulate the bandwidth since the silicon grating features a wide bandwidth.The gratings are cascaded in the design.In the experimental process,variable parameters such as the depeth of grating teeth,the distance between the gratings,and the length of the coupling area,are analyzed to obtain a narrow bandwidth.The measurement results show that passbands of the drop ports exhibit a 20 dB bandwidth of 0.8 nm and an insertion loss of 2.6 dB.3.A four-channel DWDM tunable add/drop demultiplexer based on silicon waveguide Bragg gratings is demonstrated.Each channel features the methods of cascading,apodization,and thermal tuning.With the aid of these measures,passbands of the four drop ports exhibit 3 dB and 20 dB bandwidths of 0.4 nm and 0.8 nm,respectively,while isolation between adjacent channels is better than 20 dB.Insertion losses at through and drop ports are 0.6 dB and-2.6 dB,respectively.The maximal wavelength-tunable range is up to 25 nm.The proposed demultiplexer can be applied in the 200GHz DWDM systems,and has the potencial for 100GHz and 400GHz DWDM systems.