Topic Code: IOC Invited Talk SILICON PHOTONICS IN SOI PLATFORM: PROBLEMS WITH WAVEGUIDE DISPERSION AND BIREFRINGENCE EFFECTS B.K. Das, Sujith C, G.R. Bhatt, U. Karthik, and R. Sharma Integrated Optoelectronics / Microelectronics & MEMS Labs Department of Electrical Engineering, IIT Madras, Chennai – 600 036, India E-Mail: bkdas@ee.iitm.ac.in Abstract: Various SOI based waveguide geometries have been studied in terms of their guided mode birefringence, mode-field distributions, bend-induced waveguide losses, and wavelength dispersions. It has been observed that the major bottleneck of CMOS compatible silicon photonics devices in DWDM applications is the waveguide birefringence and group index dispersion effects. 1. INTRODUCTION Compact, light-weight, cost-effective, multifunctional and efficient PIC/OEIC can be realized in SOI platform by integrating various photonic and electronic components via low-loss, broad-band and high-speed optical interconnects or tightly confined single-mode optical waveguides [1]. However, these waveguides are found to be highly dispersive as well as polarization dependent and consequently limiting the device performances. In an effort to eliminate/compensate these discrepancies, we have studied various single-mode waveguide geometries in terms of guided mode birefringence, mode-field distributions, bend-induced waveguide losses, and wavelength dispersions. 2. SINGLE-MODE SOI WAVEGUIDES Based on literature reports, we have classified four different types of single-mode SOI waveguides (see Table-I): (i) LCRW – large cross-section rib waveguide, (ii) RCRW – reduced cross-section rib waveguide, (iii) PhWRW – photonic wire rib waveguide, and (iv) PhWW – photonic wire waveguide. First two types of waveguides are compatible to microelectronics & MEMS technology whereas the last two types are CMOS compatible. Fig. 1: Typical waveguide cross-sectional view in SOI platform: W – waveguide width, H – device layer thickness, and h – slab height. Our theoretical investigations reveal that both LCRW and RCRW are nearly polarization independent and dispersion free. However, PhWRW and PhWW are found to be highly polarization sensitive and dispersive. Currently, we are working towards designing a polarization insensitive and dispersion free silicon photonics devices based on optimized photonic wire waveguide geometry. Table–I: Various single-mode waveguide parameters and group index dispersion (GID) at λ = 1550 nm. W [μm] H [μm] h [μm] GID [nm -1 ] TE TM LCRW 5.0 5.0 3.2 -2×10 -8 -2×10 -8 RCRW 1.3 2.0 0.8 -2×10 -6 -2×10 -6 PhWRW 0.5 0.22 0.05 -6×10 -4 -9×10 -4 PhWW 0.5 0.22 0 -9×10 -4 -1×10 -3 3. EXPERIMENTAL RESULTS We have successfully demonstrated single-mode LCRW and RCRW waveguide structures using conventional microelectronics technology. The LCRW structures were fabricated by single-step RIE process [2], whereas, the RCRW by a multi-step RIE process. As expected, they have been characterized as nearly polarization independent. The wavelength dependent performances of some fabricated integrated optical devices based on these waveguide geometries are being investigated and will be presented during the conference. RCRW structures are found to be technologically rugged in bio-sensing applications. 4. CONCLUSIONS We have investigated the properties of various single- mode waveguide geometries in SOI platform. Polarization dependencies and wavelength dispersion appear to be the real bottleneck for CMOS compatible silicon optical interconnects. Wavelength dependent device performances will be presented. REFERENCES [1] K. Ohira, et al, “On-chip optical interconnection by using integrated III-V laser diode and photodetector with silicon waveguide”, Opt. Express, vol. 18, pp. 15440 – 15447, 2010. [2] R. Navalakhe, et al, “Fabrication and characterization of straight and compact S-bend optical waveguides on a silicon-on-insulator platform”, Appl. Opt., vol. - 48, G125-130, 2009.