Chemically synthesized metal nanowires are promising building blocks for next-generation photonic integrated circuits, but technological implementation in monolithic integration will be severely hampered by the lack of controllable and precise manipulation approaches, due to the strong adhesion of nanowires to substrates in non-liquid environments. Here, we demonstrate this obstacle can be removed by our proposed earthworm-like peristaltic crawling motion mechanism, based on the synergistic expansion, friction, and contraction in plasmon-driven metal nanowires in non-liquid environments. The evanescently excited surface plasmon greatly enhances the heating effect in metal nanowires, thereby generating surface acoustic waves to drive the nanowires crawling along silica microfibres. Advantages include sub-nanometer positioning accuracy, low actuation power, and self-parallel parking. We further demonstrate on-chip manipulations including transporting, positioning, orientation, and sorting, with on-situ operation, high selectivity, and great versatility. Our work paves the way to realize full co-integration of various functionalized photonic components on single chips.

Although monolayer transition metal dichalcogenides (TMDs) have direct bandgaps, the low room-temperature photoluminescence quantum yields (QYs), especially under high pump intensity, limit their practical applications. Here, we use a simple photoactivation method to enhance the room-temperature QYs of monolayer MoS2 grown on to silica micro/nanofibers by more than two orders of magnitude in a wide pump dynamic range. The high-density oxygen dangling bonds released from the tapered micro/nanofiber surface are the key to this strong enhancement of QYs. As the pump intensity increases from 10−1 to 104 W cm−2, our photoactivated monolayer MoS2 exhibits QYs from ~30 to 1% while maintaining high environmental stability, allowing direct lasing with greatly reduced thresholds down to 5 W cm−2. Our strategy can be extended to other TMDs and offers a solution to the most challenging problem toward the realization of efficient and stable light emitters at room temperature based on these atomically thin materials.

Since the discovery of graphene, 2D atomic layered materials, including graphene and transition metal dichalcogenide (TMD) materials, have attracted significant interest because of their extraordinary optical and electrical properties compared to their bulk materials counterparts. [1][2][3][4] Among these properties, nonlinear optical effects in 2D atomic layered materials (such as TMD) have been intensively investigated, e.g., crystal orientation dependence, boundary effects, stacking order dependent crystal evolution, or charge-induced secondharmonic (SH) generation. [3,[5][6][7][8] In particular, layered GaSe structures have revealed superior nonlinear optical properties, with the strongest nonresonant SH generation among all the ever-reported 2D atomic crystals. [9,10] Historically, bulk GaSe has been widely used for nonlinear optical frequency conversion at near and midinfrared wavelengths, such as generation of terahertz radiation. [11] It was noted that by reducing the dimensionality to 2D, the extra requirement for achieving phase matching could be eliminated conside ring that the atomic thickness is much less than the coherence length. [12] However, 2D materials, considering their physical atomic thickness (≈1 nm), are not suitable for efficient nonlinear optical interactions because of the limited light-matter interaction length.To address this problem, waveguiding excitation in micro/ nanowaveguides is proposed to significantly enhance the lightmatter interaction via the long propagation distance, which has been demonstrated in a variety of materials, such as polymers, semiconductors, metals, and upconversion nanocrystals, [13][14][15] suggesting a promising approach for enhanced nonlinear optical applications. [16,17] Nevertheless, to the best of our knowledge, use of GaSe nanowaveguides for nonlinear frequency conversion has not yet been demonstrated. In this work, high-quality single-crystal GaSe nanoribbons (NRs) are successfully fabricated and demonstrated as waveguides with good performance. By taking advantage of the strong confinement and long interaction length of the waveguiding approach, significantly enhanced nonlinear light-matter interaction is observed in GaSe NRs. Based on transverse SH generation, a single GaSe NR-configured Layered GaSe flakes have revealed strongest second-harmonic (SH) generation among all the two-dimensional (2D) atomic crystals measured up to now. However, the unique feature of physical atomic thickness at nanometer scale prevents their practical applications in efficient nonlinear optical conversion due to limited light-matter interaction length. In this work, high quality single-crystal GaSe nanoribbons (NRs) are fabricated and demonstrated as waveguides with good performance. By taking advantage of the strong confinement and long interaction length of the waveguiding approach, significantly enhanced nonlinear light-matter interaction is observed in GaSe NRs. Based on transverse SH generation, a single GaSe NR-configured optical auto-correlator is constructed fo...

Stimulating higher-order nonlinear optical (HO-NLO) response from individual semiconductor nanostructures is challenging due to the low nonlinear coefficients and the small number of molecules within the nanostructures. In this work, we demonstrate efficient third harmonic generation and multi-photon luminescence in CdSe nanowaveguides by means of evanescent wave coupling technique. Under appropriate conditions, a coupling efficiency of 70% can be achieved from an optical microfiber to a single CdSe nanowaveguide, leading to the enhanced HO-NLO effects. Provided a high signal-to-noise ratio, we thus observe a fourth order excitation power dependence of 3-photon luminescence, and we attribute it to surface defect mechanism based on the recombination of free carriers. This work provides an alternative for efficient excitation for HO-NLO, which also makes these hard-to-produce signals more feasible in the applications of nonlinear optical devices.

The exploration relevant to the surface changes on optical micro- and nanofibers (MNFs) is still in infancy, and the reported original mechanisms remain long-standing puzzles. Here, by recognizing the combined interactions between fiber heating, mechanically tapering, and high-power pulsed laser guiding processes in MNFs, we establish a general thermal-mechanical-photo-activation mechanism that can explain the surface changes on MNFs. Our proposed activation mechanism can be well supported by the systematical experimental results using high-intensity nanosecond/femtosecond pulsed lasers. Especially we find large bump-like nanoscale cavities on the fracture ends of thin MNFs. Theoretically, on the basis of greatly increased bond energy activated by the fiber heating and mechanically tapering processes, the energy needed to break the silicon-oxygen bond into dangling bonds is significantly reduced from its intrinsic bandgap of ∼9 eV to as low as ∼4.0 eV, thus high-power pulsed lasers with much smaller photon energy can induce obvious surface changes on MNFs via multi-photon absorption. Finally, we demonstrate that using surfactants can repair the MNF surfaces and exploit them in promising applications ranging from sensing and optoelectronics to nonlinear optics. Our results pave the way for future preventing the performances from degradation and enabling the practical MNF-based device applications.