Tunable nanowire nonlinear optical probe

Abstract

One crucial challenge for subwavelength optics has been the development of a tunable source of coherent laser radiation for use in the physical, information and biological sciences that is stable at room temperature and physiological conditions. Current advanced nearfield imaging techniques using fibre-optic scattering probes 1,2 have already achieved spatial resolution down to the 20-nm range. Recently reported far-field approaches for optical microscopy, including stimulated emission depletion 3 , structured illumination 4 , and photoactivated localization microscopy 5 , have enabled impressive, theoretically unlimited spatial resolution of fluorescent biomolecular complexes. Previous work with laser tweezers 6-8 has suggested that optical traps could be used to create novel spatial probes and sensors. Inorganic nanowires have diameters substantially below the wavelength of visible light and have electronic and optical properties 9,10 that make them ideal for subwavelength laser and imaging technology. Here we report the development of an electrode-free, continuously tunable coherent visible light source compatible with physiological environments, from individual potassium niobate (KNbO 3 ) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.Nanometre-scale photonics is emerging as a key ingredient in novel sensing and imaging applications, as well as for advanced information technology, cryptography, and signal processing circuits. A versatile and useful nonlinear circuit element for integrated optical networks must be able to double the frequency of light using second harmonic generation (SHG), a second-order nonlinear optical phenomenon. In this process, two photons with the fundamental angular frequency v 1 are converted through a nonlinear crystal polarization into a single photon v 2 at twice the fundamental frequency (v 2 5 2v 1 , the field still lacks sufficiently small devices that efficiently generate tunable coherent photons. Here we show that the large second-order susceptibility x (2) of KNbO 3 nanowires facilitates the generation of tunable, coherent visible radiation that is sufficient for in situ scanning and fluorescence microscopy.We chose the perovskite oxide KNbO 3 as the nanowire material because of its low toxicity, chemical stability, large effective nonlinear optical coefficients (d eff 5 10.8-27 pm V 21 at l 5 1,064 nm) at room temperature (298 K) 19 , large refractive indices (n 5 2.1-2.5) 20 , as well as its transparency in a wide range of wavelengths including the visible spectral region 21 . Single-crystalline KNbO 3 nanowires were synthesized usi...

Design of Nanowire Optical Cavities as Efficient Photon Absorbers

“…[10][11] In addition, semiconductor NW photovoltaics (PV) are emerging as a promising platform for the next generation solar cells that require a high efficiency at costs approaching grid parity. [12][13][14][15][16][17][18][19] In particular, p/i/n core-shell NWs demonstrate electrical and optical properties distinct from conventional planar materials: radial minority carrier separation with short diffusion lengths, and enhanced light absorption resulting from the cavities' subwavelength size.…”

Nonlinear Optical Response in Single Alkaline Niobate Nanowires

“…In addition, the latest experiments 10 demonstrated that these nanostructures can be used as local mechano-optical probes. 11,12 Although many groups report on the synthesis and structural characterization of different types of alkaline niobate nanowires, there are no comparative studies that address their nonlinear optical response. In this work, we compare SHG signal and waveguiding properties for three types of perovskite alkaline niobate nanowires such as NaNbO 3 , KNbO 3 , and LiNbO 3 (XNbO 3 ).…”

Movable high-Q nanoresonators realized by semiconductor nanowires on a Si photonic crystal platform

“…With our proposed design, we can add various III/V functional nanocavity devices at arbitrary positions in Si waveguides. From another viewpoint, NW photonic devices generally suffer from poor input/output coupling [6][7][8][9][10][11]13 , but with our present configuration the NW cavity mode can be easily coupled to Si photonics waveguides as already demonstrated for a simple waveguide 23 .…”

“…A variety of structures, including core-shell 2 , multi-layer heterostructures [3][4][5] , and p-i-n junctions 6,7 , have been implemented specifically for III/V semiconductor NWs by appropriately arranging the growth sequence. Several interesting NW photonic devices have been reported, such as lasers [8][9][10][11] , light-emitters 6 , single photon source 12 , photo-detectors 7 , and wavelength converters 13 . The dimensions of the NWs naturally suggest that NW-based photonic devices are promising for ultrasmall and power-efficient device operation 14 .…”