Simulation Study of Stress Effect on Performance and Design Methodology of Proposed Si/SiGe Integrated Bragg Grating Filter

The stress-induced due to thermal and intrinsic mismatch between different layers in silicon photonic devices critically affect the device performance. This makes the inclusion of stress while designing such devices absolutely necessary to ensure reliable and predictable operation of the eventually fabricated device. In this regard, this paper presents the design methodology of a proposed Si/SiGe integrated Bragg grating (IBG) filter that includes the influence of stress effect during filter design. Moreover, it also reports the variation in the optical performance of the device due to stress effect. The methodology utilizes both analytical and numerical approaches. IBG filters realized over SOI platform are designed using the proposed method for C-band of operation and having different 3-dB bandwidths. Refractive index variation along the length of the proposed filter has been achieved by introducing SiGe alloy filled grooves, which are corrugated in silicon strip waveguide. The efficacy of the methodology has been demonstrated for varying waveguide width and three different Ge fractions, i.e., 0.10, 0.15 and 0.20 in SiGe. The stress at Si-SiGe interface due to the lattice and thermal mismatch has been incorporated in a modified transfer matrix method (TMM), which is in its unmodified form can only be used under no-stress condition. The proposed design methodology has been tested for designing three IBG filters having 10 nm, 5 nm and 1.6 nm bandwidths along with other suitable user-defined parameters; such as maximum insertion loss (IL), minimum extinction ratio (ER), Ge fraction in SiGe alloy, and center wavelength. It has been found that our proposed methodology, which is based on modified TMM, can find possible combinations of width, length, SiGe groove depth of the IBG filters that meet user-defined specifications even in presence of stress. This paper also compares the results generated by the proposed modified TMM with the results from commercially available photonic device design tool. It has been found that the proposed method can result IBG filters having estimated optical performances with an accuracy of < 10%, <8%, and <0.01% for ER, bandwidth, and resonance wavelength, respectively.