We investigate a cadmium sulfide (CdS) nanowire (NW) laser that is spontaneously internalized into a single cell to serve as a stand-alone intracellular probe. By pumping with nano-joule light pulses, green laser emission (500-520 nm) can be observed inside cells with a peak linewidth as narrow as 0.5 nm. Due to the sub-micron diameter (∼200 nm), the NW has an appreciable fraction of the evanescent field outside, facilitating a sensitive detection of cellular environmental changes. By monitoring the lasing peak wavelength shift in response to the intracellular refractive index change, our NW laser probe shows a sensitivity of 55 nm per RIU (refractive index units) and a figure of merit of approximately 98.

By integrating a free-standing cadmium sulfide (CdS) nanowire onto a silicon nitride (SiN) photonic chip, we demonstrate a highly compact on-chip single-mode CdS nanowire laser. The mode selection is realized using a Mach-Zehnder interferometer (MZI) structure. When the pumping intensity exceeds the lasing threshold of 4.9 kW/cm 2 , onchip single-mode lasing at~518.9 nm is achieved with a linewidth of 0.1 nm and a side-mode suppression ratio of up to a factor of 20 (13 dB). The output of the nanowire laser is channelled into an on-chip SiN waveguide with high efficiency (up to 58%) by evanescent coupling, and the directional coupling ratio between the two output ports can be varied from 90 to 10% by predesigning the coupling length of the SiN waveguide. Our results open new opportunities for both nanowire photonic devices and on-chip light sources and may pave the way towards a new category of hybrid nanolasers for chip-integrated applications.

and techniques have been proposed and/ or developed. Here we focus on a newly emerging area-plasmonic nanolaser that pursuing extremely smaller cavity size in one or more dimensions, and consequently extreme lasing conditions, by using a plasmonic cavity with feature size possibly far below the diffraction limit of light.The miniaturization of a laser can be traced back to the early age of the laser, when compact semiconductor structures were introduced. In particular, the introduction of semiconductors as the gain media in 1962, [11,12] followed by a series of elaborately engineered structures from heterostructure, [13] quantum well, [14] vertical-cavity surface-emitting laser (VCSEL), [15,16] microdisk, [17][18][19] photonic crystal, [20][21][22] quantum dot [23,24] to nanowire (NW) [25][26][27] have made great success in shrinking a laser from bulk scale to wavelength level using reduced cavity sizes. [28] For example, to date, typical commercial edgeemitting quantum well laser diodes have dimensions of several micrometers in width and hundreds of micrometers in length, and a single quantum dot can lase in a photonic crystal cavity with overall dimension of merely 0.7(λ/n) 3 , where λ is the vacuum wavelength and n the refractive index of the dielectric. [29] With optimized geometry and material for cavity design, lower structural dimension is expected. However, in a dielectric cavity with limited refractive index n, the cavity size is intrinsically restricted by optical diffraction limit that sets an ultimate limit λ/2n for both cavity length and mode size in all three dimensions.An effective step to shrink a cavity beyond the diffraction limit is converting light into surface plasmon polaritons (SPPs) in nanostructuralized metals, which is a kind of collective oscillation of quasi free electrons on the interface of a metal and a dielectric. [30] While SPP is featured with ultrahigh optical confinement and ultrafast relaxation process as shown in Figure 1a, [31] it is inevitably accompanied by ultrahigh energy dissipation (i.e., Ohmic loss), leading to a mutual balance between the mode size and the optical loss in either a nanowaveguide or a nanocavity as shown in Figure 1b. [32] For example, the transverse mode area of SPP mode on an Ag nanowire with diameter of 100 nm can be as small as 0.01 µm 2 but also exhibits a propagation loss larger than 200 dB mm −1 . Despite of the high loss coefficient of plasmonic resonance at optical frequency, a properly designed nanoplasmonic cavity coupled with a gain medium is possible to lase with miniature cavity length.Owing to their ultrahigh optical confinement, plasmonic nanolasers with cavity sizes beyond the diffraction limit of light, are attracting increasing attention for pursuing extreme lasing conditions on nanoscale including ultracompact cavity mode, ultrafast lasing modulation, significantly enhanced light-matter interaction, and Purcell effect. In this review, the recent progress on plasmonic nanolasers from both theoretical and experimental aspects is intro...

Ice is known to be a rigid and brittle crystal that fractures when deformed. We demonstrate that ice grown as single-crystal ice microfibers (IMFs) with diameters ranging from 10 micrometers to less than 800 nanometers is highly elastic. Under cryotemperature, we could reversibly bend the IMFs up to a maximum strain of 10.9%, which approaches the theoretical elastic limit. We also observed a pressure-induced phase transition of ice from Ih to II on the compressive side of sharply bent IMFs. The high optical quality allows for low-loss optical waveguiding and whispering-gallery-mode resonance in our IMFs. The discovery of these flexible ice fibers opens opportunities for exploring ice physics and ice-related technology on micro- and nanometer scales.

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By placing a single Au nanoparticle on the surface of a cadmium sulfide (CdS) nanowire, we demonstrate strong coupling of localized surface plasmon resonance (LSPR) modes in the nanoparticle and whispering gallery modes (WGMs) in the nanowire. For a 50-nm-diameter Au-nanosphere particle, strong coupling occurs when the nanowire diameter is between 300 and 600 nm, with a mode splitting up to 80 meV. Using a temperature-induced spectral shift of the resonance wavelength, we also observe the anticrossing behavior in the strongly coupled system. In addition, since the Au nanosphere has spherical symmetry, the supported LSPR mode can be selectively coupled with transverse electric (TE) and transverse magnetic (TM) WGMs in the nanowire. The ultracompact strong-coupling system shown here may provide a versatile platform for studying hybrid “photon–plasmon” nanolasers, nonlinear optical devices, and nanosensors.

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Mode-locked Yb-doped fiber lasers around 1 μm are attractive for high power applications and low noise pulse train generation. Mode-locked fiber lasers working in soliton and stretched-pulse regime outperform others in terms of the laser noise characteristics, mechanical stability and easy maintenance. However, conventional optical fibers always show a normal group velocity dispersion around 1 μm, leading to the inconvenience for necessary dispersion management. Here we show that optical microfibers having a large anomalous dispersion around 1 μm can be integrated into mode-locked Yb-doped fiber lasers with ultralow insertion loss down to −0.06 dB, enabling convenient dispersion management of the laser cavity. Besides, optical microfibers could also be adopted to spectrally broaden and to dechirp the ultrashort pulses outside the laser cavity, giving rise to a pulse duration of about 110 fs. We believe that this demonstration may facilitate all-fiber format high-performance ultrashort pulse generation at 1 μm and may find applications in precision measurements, large-scale facility synchronization and evanescent-field-based optical sensing.