Photonic integrated circuits (PIC) find applications in the fields of microwaves, telecoms and sensing. Generally, PICs are fabricated on a base of isotropic materials such as SOI, Si3N4, etc. However, for some applications, anisotropic substrates such as LiNbO3 are used. A thin film of LiNbO3 on an insulator (LNOI) is a promising material platform for complex high-speed PICs. The design and simulation of PICs on anisotropic materials should be performed using rigorous numerical methods based on Maxwell’s equations. These methods are characterized by long calculation times for one simulation iteration. Since a large number of simulation iterations are performed during the PIC design, simulation methods based on approximations should be used. The effective index method (EIM) is an approximation-based method and is widely applied for simulations of isotropic waveguides. In this study, the applicability of EIM for simulations of anisotropic waveguides is analyzed. The results obtained by EIM are compared with the calculation results of a rigorous finite-difference frequency-domain (FDFD) method for evaluation of the EIM’s applicability limits. In addition, radiation losses in waveguides with rough sidewalls are estimated using the Payne–Lacey model and EIM. The results demonstrate the applicability of EIM for the simulation of anisotropic LNOI-based waveguides with cross-section parameters specified in this paper.

In this study, the technology for producing ridge waveguides with a minimal roughness of the sidewalls and material surface in a near-waveguide region was developed with the purpose of fabricating miniature photonic integrated circuits on a LiNbO3 substrate. Plasma etching processes were used for the ridge waveguide fabrication on different material substrates. The specifications of the equipment and plasma source, method of mask fabrication and substrate material determined the process conditions for producing ridge waveguides with minimal sidewall roughness. In this work, for the ridge waveguide fabrication, the processes of reactive ion etching of LiNbO3 with a chromium mask were carried out in a mixture of SF6/Ar with an ICP/TCP plasma source. The process of plasma etching the LiNbO3 with the ICP/TCP plasma source is not well studied, especially for integrated photonics purposes. As a result of our experimental work, the narrow ranges of technological parameters suitable for producing ridge waveguides on LiNbO3 with smooth sidewalls, a slope angle of 60°–75° and a minimal quantity of observed defects in the near-waveguide region were identified. A model explaining the kinetics of the etching process of LiNbO3 in SF6/Ar plasma as a physical-chemical process was proposed.