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.

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.

Subject of study. Using a ring resonator as an example, this paper describes the general operating principle for optical resonators, the characteristics of such resonators, and the relationship between resonator quality factor Q and gyroscope sensitivity. Several sensor devices (optical resonators) were compared for use in the development of a miniature resonant optical gyroscope. These optical resonators were of three different types: a fiber-optic resonator, a whispering gallery mode resonator, and an integrated optical resonator ring. Methodology. The fiber-optic resonator consists of two fiber-optic splitters spliced together, the whispering gallery mode resonator consists of a three-dimensional dielectric structure in which whispering gallery modes are excited, and the integrated optical resonator ring consists of an optical waveguide and closed loop mounted on a common substrate. The characteristics of the high-Q(Q=10⁶−10⁹) whispering gallery mode resonators and fiber-optic resonators were measured using a narrow-band scanning laser and an oscillograph. A simpler approach, with a broadband laser source and an optical spectrum analyzer, was used for the low-Q(Q<10⁶) integrated optical resonators. Main results. Values of Q=5.2×10⁸, Q=4.3×10⁶, and Q=1.1×10⁴ were obtained for a MgF₂ disk resonator, fiber-optic disk resonator, and integrated optical resonator, respectively. Practical significance. The whispering gallery mode resonator turns out to be the most promising of these sensor devices since it has the highest Q and the highest accuracy for angular velocity measurements. Fiber optic resonators are competitive but are more sensitive to temperature and external mechanical effects. Integrated optical resonators have the advantage of miniaturization and the ability to include temperature stabilization components and components that provide resistance to mechanical effects.