Design of narrow bandwidth Si3N4 stressor cladded cascaded IBG filter

In this paper design and performance estimation of a narrow-band optical filter operating at 1550 nm is presented. The narrowband filter consists of cascaded integrated Bragg grating (IBG) filters each having periodic Si3N4 cladding on silicon strip waveguide based on SOI platform. The filter design also includes the effect of stress, which is generated at the Si-Si3N4 interface on their optical performance. The design of the proposed filter for a set of target specifications such as centre wavelength, bandwidth (BW), extinction ratio (ER), insertion loss (IL), and side-lobe suppression ratio (SLSR) has been done using the conventional transfer matrix method (TMM) in absence of stress and also using a modified TMM (MTMM), which is suitable for filter designs in presence of stress. It has been demonstrated in this work that using cascaded IBG filters narrowband operation can be achieved along with wideband operation. The efficacy of the proposed filter structure has been demonstrated for two different 3-dB bandwidths of 15 nm and 1.6 nm. The study reveals that the filter, which is designed using conventional TMM for a set of target specifications, shows similar optical performance when estimated using finite-element method (FEM) in absence of stress. In presence of stress, conventional TMM method fails to design the cascaded IBG filter that shows dissimilar performance when analysed using FEM. Under stressed condition, the proposed MTMM is found to design the cascaded IBG filter effectively exhibiting similar performance when tested using FEM. The study reveals that in presence of stress the MTMM can design filter, which offers deviation of <5.8%, <4.97%, <0.01% and <6.3% for ER, BW, resonance wavelength and side-lobe suppression ratio, respectively; from the FEM estimated filter performance, for a given set of targeted specifications.