Integration of Two-Dimensional and Three-Dimensional Optical On-Chip Waveguides

This paper considers the possibility of integrating two-dimensional and three-dimensional waveguides on an optical chip. The waveguide material for planar elements is silicon nitride (Si3N4), that could be used to create photonic devices with low losses in the IR spectrum. The infra-red radiation wavelength is about 1550 nm. The refractive index of silicon nitride in this wavelength is n = 1.98. The silicon nitride was chosen since planar optical elements from it can be produced using electron-beam lithography in laboratory conditions. Thus, silicon nitride can be used to manufacture optical chips and be used there as a waveguide core, with air and silicon oxide as a shell. Electron-beam lithography allows producing two-dimensional optical chips only. In practice, for providing and outcoupling radiation from an optical chip, as well as for transmitting radiation between the individual functional elements of the chip, optical bridges are required. In this paper, a new approach is used for the creation of 3-dimensional nano-bridges (waveguides) with known spatial and optical characteristics by using two-photon lithography — Direct Laser Writing (DLW). This method allows to produce a 3-dimensional waveguide from a polymeric material over the planar elements of an optical chip, providing the required optical connections. For the purpose of the study, a mathematical model that allows to determine the optical characteristics of a planar and 3-dimensional waveguide connection was developed, as well as practical laboratory experiments on the fabrication and measurement of the characteristics of planar waveguide connections using 3-dimensional waveguides - bridges for radiation transmission. Experiments have confirmed that the proposed DLW method for manufacturing three-dimensional nano waveguides is very perspective, since it has a high resolution of 100 nm. and at the same time it’s print speed is relatively high.