Moon, Sunghyun Lee, Jinil Lee, Junhyung Koh, Youngseo Kim, Changhyun Jang, Hyeong-Soon Kim, Sangin Han, Sang-Wook Jung, Hojoong Kwon, Hyounghan 2025-11-13T08:39:36Z 2025-11-13T08:39:36Z 2025-11-11 2025-06 2327-9125 https://pubs.kist.re.kr/handle/201004/153448 The integrated quantum interferometer has provided a promising route for manipulating and measuring quantum states of light with high precision, requiring negligible optical loss, broad bandwidth, robust fabrication tolerance, and scalability. In this paper, a rapid adiabatic coupler (RAC) is presented as a compelling solution for implementing the integrated quantum interferometer on a thin-film lithium niobate (TFLN)-based platform, enabling a compact, broadband, and low-loss optical coupler. The TFLN-based RACs are carefully designed by manipulating a curvature along the structures with consideration of inherent birefringence as well as fabrication-induced slanted sidewalls. The high extinction ratio over 20 dB of the RAC-based Mach-Zehnder interferometer (MZI) is achieved in the wavelength range from 1500 to 1600 nm. The beam splitter (BS) with the balanced splitting ratio is exploited for observation of on-chip Hong-Ou-Mandel (HOM) interference with high visibility of 99.25%. We believe TFLN-based RACs hold great potential to be favorably utilized for integrated quantum interferometers, enabling widespread adoptions in myriad applications in integrated quantum optics. (c) 2025 Chinese Laser Press English OSA Publishing Broadband thin-film lithium niobate rapid adiabatic couplers enabling highly visible two-photon interference Article 10.1364/PRJ.550799 1 Photonics Research, v.13, no.6, pp.1579 - 1590 Photonics Research 13 6 1579 1590 Y scie scopus 001605010000014 2-s2.0-105007068943 Optics Optics Article OU-MANDEL INTERFERENCE OPTICS