Graphene is an optical material of unusual characteristics because of its linearly dispersive conduction and valence bands and the strong interband transitions. It allows broadband light-matter interactions with ultrafast responses and can be readily pasted to surfaces of functional structures for photonic and optoelectronic applications. Recently, graphene-based optical modulators have been demonstrated with electrical tuning of the Fermi level of graphene. Their operation bandwidth, however, was limited to about 1 GHz by the response of the driving electrical circuit. Clearly, this can be improved by an all-optical approach. Here, we show that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼ 2.2 ps, limited only by the intrinsic carrier relaxation time of graphene. This modulator is compatible with current high-speed fiber-optic communication networks and may open the door to meet future demand of ultrafast optical signal processing.

We demonstrate single-mode laser emission in single nanowires. By folding a 200 nm diameter CdSe nanowire to form loop mirrors, single-mode laser emission around 738 nm wavelength is obtained with line width of 0.12 nm and low threshold. The mode selection is realized by the vernier effect of coupled cavities in the folded nanowire. In addition, the loop structure makes it possible to tune the nanowire cavity, opening an opportunity to realize a tunable single-mode nanowire laser.

High-quality quantum-dot/polystyrene nanofibers (QD/PS NFs) are synthesized by drawing solvated PS doped with CdSe/ZnS QDs. As-drawn QD/PS NFs offer ultra-long-term photostability, flexibility, and excellent optical properties for sensing applications. Based on these active NFs, optical humidity sensors with extremely low power consumption, fast response, and long-term stability are successfully demonstrated, which may lead to a new category of nanometer-scale optical sensors.

Designing lasing wavelengths and modes is essential to the practical applications of nanowire (NW) lasers. Here, according to the localized photoluminescence spectra, we first demonstrate the ability to define lasing wavelengths over a wide range (up to 119 nm) based on an individual bandgap-graded CdSSe NW by forward cutting the NW from CdSe to CdS end. Furthermore, free spectral range (FSR) and modes of the obtained lasers could be controlled by backward cutting the NW from CdS to CdSe end step-by-step. Interestingly, single-mode NW laser with predefined lasing wavelength is realized in short NWs because of the strong mode competition and increase in FSR. Finally, the gain properties of the bandgap-graded NWs are investigated. The combination of wavelength and mode selectivity in NW lasers may provide a new platform for the next generation of integrated optoelectronic devices.

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.