Microresonators in Lithium Niobate Thin Films

Abstract

geometries of microcavities supporting "whispering gallery modes" (WGMs) the light field can be confined in extremely small volumes, reaching very high power density and very narrow spectral linewidth. As a result, the ultrahigh in-cavity intensities significantly enhance the photon-tophoton interactions, leading to ultrahigh efficiencies of nonlinear optical process even at low-power optical excitation. In addition, the small scale enables the construction of resonator-based functional devices with very high integration. With combination of these intriguing features, low-power-consumption, low-cost on-chip devices can be developed successfully. The material platforms for microresonators are crucial for the practical applications. For example, silicon dioxide (SiO 2 ) is considered as one of the most commonly used materials for microresonators, and great success has been achieved based on this easy-to-fabricate platform. [29,30] Recently, with the well-developed technology for on-chip circuits fabrication, some semiconductor materials have been harnessed as the platforms of microresonators for more electro-optic potentials, such as silicon (Si), [31,32] SiC, [33][34][35][36] ZnO, [37,38] GaN, [39,40] or AlN [41,42] . Among them, lithium niobate (LiNbO 3 or LN) has risen into the forefront of microresonator demonstrations and drawn extensive interests in photonics and electronics.Lithium niobate is a multi-functional dielectric crystal that combines a number of excellent features, [43] such as electrooptic, nonlinear optical, acousto-optic, ferroelectric, piezoelectric, photorefractive, photo-luminescent properties, and receives a broad variety of applications in telecommunication, frequency conversion, optical storage, filtering, and quantum photonics. [44][45][46][47] The single-crystal thin film of LN is an ideal platform for microresonators owing to the unique combination of various excellent properties of the bulk. The major obstacle of the LN-based microcavities was the fabrication of high-quality LN thin films because the single-crystalline features cannot be well-preserved in thin-film LN produced by chemical methods of normal deposition that is applied for semiconductors. In addition, large-scale LN-thin film wafers are desired for further processing of on-chip devices. Recently, the so-called "lithium niobate on insulator" (LNOI) technology figures the major problem out and boosts the rapid development of the thin-film LN based devices. [48][49][50][51][52][53] Most used LN films are manufactured by smart " Ion cut" technique. The typical commercialized LN thin film based on ion cut consists of a single-crystalline LN thin film with thickness of 300-900 nm, a cladding layer of SiO 2 with thickness of 2-3 µm, and the supporting material (LN or Si bulk wafer). The fabrication process of ion-cut LN thin film can be referenced in details elsewhere. [54][55][56] The refractive Leveraging the outstanding nonlinear optical properties and the ultra-high spatial confinement of light, microresonators based on lith...

Collective Coupling of 3D Confined Optical Modes in Monolithic Twin Microtube Cavities Formed by Nanomembrane Origami

“…16−20 In general, to construct the optical coupling systems, two or more WGM microcavities (e.g., microtoroids, 21,22 microdisks, 23,24 microrings, 25,26 microspheres 27,28 ) are placed in close proximity to explore the WGM optical coupling. 29 The WGM optical resonance is confined within a two-dimensional (2D) azimuthal plane. 30,31 The corresponding coherent coupling is constrained to a tangent site between neighboring microcavities, where the single channel of energy exchange severely hinders the parallel processing of photonic signals.…”

“…Strong interactions between coupled optical microcavities provide an intriguing platform to manipulate photons in terms of frequency and spatial distribution, − finding many unique photonic applications in a variety of fields, such as nonlinear optics, , laser physics, , and non-Hermitian photonics. − Whispering-gallery-mode (WGM) microcavities supporting resonances along a ring trajectory have been identified as ideal candidates for building those coupled microcavity systems and investigating resonant optical coupling phenomena. − The strong interactions between two resonant modes can arise from the surface backscattering or nonlinear coupling in a single WGM microcavity. − In general, to construct the optical coupling systems, two or more WGM microcavities (e.g., microtoroids, , microdisks, , microrings, , microspheres , ) are placed in close proximity to explore the WGM optical coupling . The WGM optical resonance is confined within a two-dimensional (2D) azimuthal plane. , The corresponding coherent coupling is constrained to a tangent site between neighboring microcavities, where the single channel of energy exchange severely hinders the parallel processing of photonic signals.…”

Fano-Resonant Metasurface with 92% Reflectivity Based on Lithium Niobate on Insulator

“…Fortunately, with the rapid development of micro/nano processing technology and the emergence of lithium niobate on insulator (LNOI) [ 4 ], researchers have proposed various processing techniques for thin-film LN, such as thermal diffusion or plasmon exchange [ 5 ], femtosecond laser direct writing [ 6 , 7 ], focused ion beam etching [ 8 ], and plasma dry etching [ 9 ]. Thanks to these advanced processing techniques, a variety of high-performance integrated photonic devices based on LNOI have been proposed, including low-loss waveguides [ 10 ], electro-optical modulators [ 11 , 12 ], micro-resonators [ 13 , 14 ], metamaterials [ 15 ], nonlinear optical devices [ 16 , 17 ], and so on. These research findings have greatly contributed to the prosperity and development of integrated photonics based on LNOI.…”

Optimized design of the lithium niobate for spectrally-pure-state generation at MIR wavelengths using metaheuristic algorithm

“…Secondly, the group-velocity-matched (GVM) wavelengths of LN crystal are intrinsically at the MIR wavelengths [15]. Thirdly, PPLN plays an important role in integrated quantum optics [16], as it possesses the characteristic of scalability and microminiaturization, which is beneficial in waveguide substrate [17][18][19] and thin-film material [20,21]. Up to now, many theoretical and experimental works have utilized PPLN as the medium to prepare the single-photon source [15,[22][23][24] or entangled photon source [25] at MIR wavelengths.…”