Recent research progresses in slot waveguide have shown that it is possible to achieve photon confinement in low-refractive index region with nm thickness. To utilize this photon confinement, we propose a multilayer waveguide that could be the optimum design for future silicon light emission devices.
Our device consists of multiple alternating layers of Si and SiO2 with nm thickness, which can be easily fabricated. Both transfer matrix method (TMM) and FDTD simulation are used to simulate the performance of this device. We calculated the propagation mode index, and photon confinement in SiO2 layers. Birefringence as high as 0.8 is achieved with moderate design parameters, although a homogeneous slab waveguide also shows some birefringence, it cannot account for the high birefringence we have calculated. Thus it indirectly indicates that for TM polarization photons are actually confined in SiO2 layers, where the refractive index is lower. Also our photon confinement simulation shows that, for a structure with multilayer region thickness of 0.52 μm, photon confinement in SiO2 layers as high as 75% can be achieved with Si/SiO2 layer thickness ratio close to 1.
We fabricated a few multilayer samples with different Si/SiO2 thickness ratios and performed M-line measurement to measure the propagation mode index. The measurement results agrees well with our simulate results, indicates that for TM polarization photons can be strongly confined in SiO2 layers in this multilayer structure. Thanks to this high confinement in SiO2 layers, this structure could be an excellent choice for future silicon light emitting devices.