Integrated optical waveguides for quantum photon gates at a wavelength of 810 nm

Abstract

Subject of study. The optical losses in waveguides designed for creating quantum photon gates at a wavelength of 810 nm were investigated. Aim of study. The aim of the study was to create integrated optical single-mode waveguides for quantum photon gates at a wavelength of 810 nm and to estimate optical losses acceptable for maintaining the necessary degree of photon-pair entanglement. Method. The waveguides were manufactured through thermal diffusion of titanium ions into a substrate composed of an X-slice of nominally pure lithium niobate (LiNbO3). Optical losses were estimated by experimentally measuring the loss per unit length of the waveguide. Optical radiation was coupled into and out of the waveguide using fiber segments, with one end connected and the other cleaved. A drop of immersion liquid was applied between the cleaved fiber and waveguide end, and measurements were performed for both polarization modes. Main results. Six groups of samples were produced, each containing waveguides with strip widths of d=3.0, 2.0, and 1.5 µm. The measured optical losses in the manufactured waveguides indicated that those with a titanium strip width of d≈3 µm exhibited the lowest losses. The estimated minimum optical losses for transverse magnetic and transverse electric polarization were approximately 0.20–0.25 and 0.1 dB/cm, respectively. Practical significance. The waveguides manufactured with a strip width of approximately 3 µm can be used to create quantum photonic gates in an integrated optical design. The chosen wavelength of 810 nm offers potential for near-future development of photonic gates, as one of the most accessible methods for generating entangled photon pairs involves using a 405-nm laser followed by wavelength doubling through a nonlinear beta-barium borate crystal.