Introduction
Fabrication and characterization of semiconductor nanowires
Optical properties of nanowires
Endface reflectivity of a nanowire
Coupling between closely contacted parallel nanowires
Fig.3 Coupling between closely contacted parallel nanowires. (a) 3D FEM simulation of light coupling between two 160 nm diameter nanowires with refractive index of 2.0; (b) couping efficiency between two nanowires with different wavelengths, couping lengths and separation distances [16] |
Substrate induced optical effects
Optically pumped nanowire lasers
Single nanowire lasers
Fig.5 Optical characterization of a 12.2 μm long 250 nm diameter ZnO semiconductor nanowire laser [29]. (a) Output spectra versus pump intensity of a ZnO nanowire laser; (b) SEM image and CCD images for the same nanowire as in (a) under different pump intensities; (c) pump intensity dependence of the total output power (circles) for the same nanowire; (d) same data and fit on log-log scale |
Microfiber coupled semiconductor nanowire lasers
Fig.6 Microfiber-knot-resonator coupled semiconductor nanowire laser [30]. (a) SEM image of attached area of 25 μm long 350 nm diameter ZnO nanowire and 780 μm diameter microfiber knot assembled with 1.8 μm diameter silica microfiber; (b) SEM image of attached area of three ZnO nanowires and 728 μm diameter silica microfiber knot assembled with 3.5 μm diameter silica microfiber, the diameters of ZnO nanowires are 500, 480, and 600 nm, respectively; (c) schematic diagram of the structure of hybrid laser. Inset: CCD image of the hybrid structure pumped by 355 nm wavelength laser pulses; (d) output spectra versus pump energy of hybrid structure (same structure shown in Fig. 1(a)); (e) and (f) close-up views of two laser spectra in (d) |
Fig.7 Microfiber coupled multicolor semiconductor nanowire laser [31]. (a) Schematic configuration of the red-green-ultraviolet three-color laser; (b) CCD image of the hybrid structure pumped by 355 nm wavelength laser pulses; (c) emission spectra of the three-color laser shown in (b) under different pump energy |
Fig.8 Pigtailed CdS nanoribbon ring laser [19]. (a) Schematic of structure of nanoribbon ring laser system; (b) optical micrographs of 20 μm diameter CdS nanoribbon ring under pumping; scale bar, 10 μm: (the nanoribbon is 600 nm wide and 330 nm thick); (c) collected lasing spectra of the nanoribbon ring. (Inset: integrated emission power versus pump energy of nanoribbon ring laser); (d) and (e) polar plots of the emission intensity from nanoribbon endfacet as a function of polarization angle, (d) front view and (e) side view. Black lines under the square represent the substrate |
Single mode nanowire lasers
Fig.9 Single mode single nanowire laser [32]. (a) PL microscope images and schematic diagrams of lasing cavities of single nanowire structures; (b) output lasing spectra of single-nanowire structures without LM; (c) with one LM, and (d) with double LMs. Inset, SEM images of the nanowire cavity corresponding to (b), (c) and (d); (e) emission power vs pump fluence of the excited NW without LM (triangle), with one LM (square), and with double LMs (circle); (f) spectral shift of the lasing peak from 733.7 to 726.9 nm by changing the geometry of the loop in a 240 nm diameter 84 μm length CdSe nanowire laser. Inset, SEM images of the original cavity (bottom right) and the changed cavity (up left) |
Fig.10 Single mode laser achieved in coupled nanowires [33]. (a) Single-mode lasing spectra of the X-coupled CdSe nanowires with pumping levels of 151.7 µJ/cm2 (blue line) and 120.8 µJ/ cm2 (gray line), respectively. Inset: CCD image of the lasing X-structure; (b) multimode lasing spectra of the individual 89 µm length CdSe nanowires. Inset: CCD image of the lasing nanowire |