Owing to their atomic layer thickness, strong light-material interaction, high nonlinearity, broadband optical response, fast relaxation, controllable optoelectronic properties, and high compatibility with other photonic structures, 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, have been attracting increasing attention for photonic applications. By tuning the carrier density via electrical or optical means that modifies their physical properties (e.g., Fermi level or nonlinear absorption), optical response of the 2D materials can be instantly changed, making them versatile nanostructures for optical modulation. Here, up-to-date 2D material-based optical modulation in three categories is reviewed: free-space, fiber-based, and on-chip configurations. By analysing cons and pros of different modulation approaches from material and mechanism aspects, the challenges faced by using these materials for device applications are presented. In addition, thermal effects (e.g., laser induced damage) in 2D materials, which are critical to practical applications, are also discussed. Finally, the outlook for future opportunities of these 2D materials for optical modulation is given.

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Wavelength tunability of lasers is one of the most important parameters for achieving practical applications such as optical communication, environmental monitoring, and spectroscopy analysis. A wide‐wavelength tunable laser is demonstrated on a single non‐doped CdSe nanowire (NW) without changing pumping intensity and position, but by simply gradually cutting the NW shorter instead. The corresponding mechanism for the large wavelength shifts is determined as the absorption‐emission‐absorption (AEA) process in polar CdSe NWs.

As a combination of fiber optics and nanotechnology, optical microfibers and nanofibers (MNFs) have been emerging as a novel platform for exploring fiber-optic technology on the micro/nanoscale. Typically, MNFs taper drawn from glass optical fibers or bulk glasses show excellent surface smoothness, high homogeneity in diameter and integrity, which bestows these tiny optical fibers with low waveguiding losses and outstanding mechanical properties. Benefitting from their wavelengthor sub-wavelength-scale transverse dimensions, wave-

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Metallic and plasmonic nanolasers have attracted growing interest recently. Plasmonic lasers demonstrated so far operate in hybrid photon-plasmon modes in transverse dimensions, rendering it impossible to separate photonic from plasmonic components. Thus only the far-field photonic component can be measured and utilized directly. But spatially separated plasmon modes are highly desired for applications including high-efficiency coupling of single-photon emitters and ultrasensitivity optical sensing. Here, we report a nanowire (NW) laser that offers subdiffraction-limited beam size and spatially separated plasmon cavity modes. By near-field coupling a high-gain CdSe NW and a 100 nm diameter Ag NW, we demonstrate a hybrid photon-plasmon laser operating at 723 nm wavelength at room temperature, with a plasmon mode area of 0.008λ(2). This device simultaneously provides spatially separated photonic far-field output and highly localized coherent plasmon modes, which may open up new avenues in the fields of integrated nanophotonic circuits, biosensing, and quantum information processing.

Integration of miniaturized elements has been a major driving force behind modern photonics. Nanowires have emerged as potential building blocks for compact photonic circuits and devices in nanophotonics. We demonstrate here a single nanowire optical correlator (SNOC) for ultrafast pulse characterization based on imaging of the second harmonic (SH) generated from a cadmium sulfide (CdS) nanowire by counterpropagating guided pulses. The SH spatial image can be readily converted to the temporal profile of the pulses, and only an overall pulse energy of 8 μJ is needed to acquire a clear image of 200 fs pulses. Such a correlator should be easily incorporated into a photonic circuit for future use of on-chip ultrafast optical technology.

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.