Hybrid 2D‐Material Photonics with Bound States in the Continuum

Abstract

dielectric materials on a 2D material followed by postfabrication of PICs with lithography methods. [19][20][21][22] The layer transfer process of 2D materials on prefabricated PICs has the potential disadvantage of introducing strain and possible distortion of the 2D lattice if the strong van der Waals attraction between the 2D material and the dielectric surface produces conformal coverage over the sharp waveguide ridge corners, leading to reduced electron mobility, more phonon scattering centers, and possible degradation of device performance. While it is possible to planarize optical waveguides by additional processing involving deposition of low-refractive-index dielectrics followed by chemical-mechanical polishing, [6,8,13,23,24] such processes will reduce the optical overlap with the 2D material. For growing and patterning thin-film dielectric materials on 2D materials, the properties of both the thin-film dielectrics and 2D materials are usually affected adversely. [25][26][27][28] For example, the excellent properties of 2D materials can be destroyed by high-energy ions during the material growth process. Although some fabrication techniques for integrating 2D materials with dielectric materials like polymers [29] and chalcogenide glass [22] produce negligible effects on the material properties, they cannot universally be applied to many other types of dielectrics on 2D materials. In addition, few 2D materials can be grown on single-crystal materials with excellent optical properties. Therefore, a generic approach for integrating any types of 2D materials with any types of singlecrystal dielectrics is highly desired.The concept of "bound states in the continuum (BICs)" was first proposed by von Neumann and Wigner in 1929 with the mathematical construction of a 3D potential which can support perfectly confined states in a continuous band. [30] The radiation loss of these confined states can be eliminated by engineering their destructive interference with the continuous modes. [31][32][33][34][35][36][37][38][39] Harnessing BICs in PICs allows for low-loss light guidance and routing with a low-refractive-index waveguide on a high-refractive-index substrate. The light guided by the low-refractive-index waveguide can be confined to a region of the high-refractive-index substrate below the low-refractive-index waveguide. [40] Because the substrate is naturally flat, transferring a 2D material onto the high-refractive-index Integration of 2D materials on dielectric planar optical waveguides can make available new functionalities from the 2D materials' enhanced optoelectronic properties, such as nonlinearity, light emission, modulation, photodetection, and saturable absorption. However, the conventional integration schemes involving either the transfer of 2D materials onto prepatterned nonplanarized topology of photonic integrated circuits (PICs) or the growth and patterning of dielectric materials on 2D materials can degrade the properties of either the dielectric or the 2D material. Here, a fundamentally new ...

Few-Layer Graphene Integrated Tilted Fiber Grating For All-Optical Switching

“…5, which can also help to reduce the response time. It is therefore possible to shorten the response time to the order of microsecond, which is consistent with the reports by using much thinner fiber or onchip device in the experiment [8,23]. Moreover, compared with schemes using geometry-modified fibers embedded in interferometers, the integration of TFBG with a few-layer graphene offers a compact, robust structure near zero insertion loss, making them easier to be incorporated into a standard fiber-optic system for all-fiber signal processing.…”

“…As a result, the cladding mode is easy to be modulated by interacting with the graphene and then fast thermo-optically induced refractive index change. The intrinsic thermal conductivity of graphene enables a very fast switching rate based on the thermal-optical effect [22,23]. In contrast with the non-resonant pump with a broadband light [16], by setting the pump wavelength at the cladding mode resonance, there is more light coupled into the graphene layer to heat the thin TFBG and endow it a highefficiency pump and fast heat-accumulation.…”

“…Hence, the thin TFBG allows the all-optical operation in a series of wavelengths where light has been coupled out of the core. Graphene has the extremely high electrical and thermal conductivity of the graphene, and then promises a very fast switching rate for all-optical switch or modulator via thermaloptic effect [22,23]. The spectrum of the TFBG could therefore be all-optically modulated.…”

High-dimensional communication on etchless lithium niobate platform with photonic bound states in the continuum

“…This concept was first proposed by von Neumann and Wigner in 1929 1 with a mathematically constructed three-dimensional potential that can support perfectly confined states in a continuous band. Recently, advancement in nanofabrication technologies has triggered fast development of BICs in photonics [10][11][12][13][14][15][16] , and the demonstrated physical phenomena are being applied to the areas of sensors 17,18 , lasers 11 , filters 19 , and integrated photonics 14,15,[20][21][22][23] . For integrated photonics, resonances can be found in a single rib waveguide without any cavity structure due to the BIC mechanism [21][22][23] .…”

“…For integrated photonics, resonances can be found in a single rib waveguide without any cavity structure due to the BIC mechanism [21][22][23] . In addition, BICs on an integrated photonic platform can be harnessed for realizing low-loss waveguiding by patterning a low-refractiveindex material on a high-refractive-index substrate 14,15,20 . Light guided by the low-refractive-index waveguide can be perfectly confined to the region of high-refractive-index substrate under the low-refractive-index waveguide.…”