Near-Field Lasing Dynamics of a Crystal-Glass Core–Shell Hybrid Fiber

Abstract

Nearly single-mode operation of a low-threshold continuous-wave crystal-glass core−shell hybrid fiber laser based on a multimode Cr 4+ :Y 3 Al 5 O 12 double-shell fiber is demonstrated. Nanoscale imaging of the optical intensity across the crystalline core allows for the direct assessment of the modal evolution, propagation modes, and near-field mode-field diameter at different working states. Below the lasing threshold of 60 mW, the near-field spatial modal distributions of the multitransverse modes are resolved and analyzed using a flattened Gaussian model. Above the threshold, nearly single-mode output with a beam quality factor of M 2 ∼ 1.1 is achieved by gain filtering, index guiding, and double-shell-based wave confinement, which are shown to agree well with the calculated light distribution.

Lasing Conditions of Transverse Electromagnetic Modes in Metallic-Coated Micro- and Nanotubes

“…Micro- and nanolasers (lasers of micro- or nanoscale dimensions) − and spasers (a type of laser that confines light at subwavelength scales by exciting surface plasmon polaritons) , can be used to provide a controllable source of “on-demand” electromagnetic fields at very small size scales . These devices can find numerous applications for enhanced spectroscopies, as a way of counteracting the effect of optical losses in different plasmonic devices, or directly as a source of radiation for “lab-on-chip” devices, ultradense data storage, or nanolithography. − Different forms of nanolasers and spasers have been extensively discussed in the literature over the last decades, both from the theoretical ,− and experimental − ,,− points of view. There has been studied a wide variety of structures and materials/metamaterials for supporting the spaser/nanolaser as well as different compounds to act as the optical-gain medium.…”

Toward Single-Mode Active Crystal Fibers for Next-Generation High-Power Fiber Devices

“…In the field of high-power active single-mode fiber devices, the exploration of materials with unique properties as relevant alternatives to existing glass-based fibers is critical to achieving further improvement in the power that such devices can carry. Crystal fiber, a typical example of the crystalline-core configuration, features exceptional optical properties in comparison to conventional glass or polymer fiber, − such as a high emission cross-section and low-threshold lasing, − high thermal loading and a high laser damage threshold, − and efficient χ (3) processes; − crystal fiber is expected to provide a key architecture for scaling the fiber laser power in the near future. Scaling fiber lasers and amplifiers to high average powers requires materials with high thermal conductivity such that heat can be easily dissipated from the interior, in this case, from the crystalline core of the fiber.…”

“…Scaling fiber lasers and amplifiers to high average powers requires materials with high thermal conductivity such that heat can be easily dissipated from the interior, in this case, from the crystalline core of the fiber. A great variety of approaches are available nowadays to fabricate such a crystalline waveguide structure, including the modification of the spatial distribution of the refractive index (RI) difference (Δ n ) within the glass and crystal matrixes by femtosecond-laser inscription − or direct crystal fiber growth by a laser-based fiber-drawing system. − , Although the former has been experimentally demonstrated to be effective for single-mode operation, the applied high-peak power often leads to a deteriorated structure, and, consequently, to a larger propagation loss, with typical values from 1 to a few dB/cm . Moreover, the employed femtosecond laser source is expensive and extremely sophisticated, making its use for practical applications difficult.…”