High-contrast wide-field evanescent wave illuminated subdiffraction imaging.

In this Letter, we show how to obtain high-contrast wide-field evanescent wave illuminated subdiffraction imaging through controlling nanoscale light-matter interaction. The light coupling, propagation, and far-field imaging processes show strong polarization selectivity and film quality dependence, which is used to improve the image-contrast-to-noise ratio (CNR) and to enlarge the field of view (FOV). We demonstrate experimentally high CNR subdiffraction imaging with lateral resolution of 122 nm and FOV of thousands of micrometers square.

Fluorescent Nanowire Ring Illumination for Wide-Field Far-Field Subdiffraction Imaging.

Here we demonstrate an active method which pioneers in utilizing a combination of a spatial frequency shift and a Stokes frequency shift to enable wide-field far-field subdiffraction imaging. A fluorescent nanowire ring acts as a localized source and is combined with a film waveguide to produce omnidirectional illuminating evanescent waves. Benefitting from the high wave vector of illumination, the high spatial frequencies of an object can be shifted to the passband of a conventional imaging system, contributing subwavelength spatial information to the far-field image. A structure featuring 70-nm-wide slots spaced 70 nm apart has been resolved at a wavelength of 520 nm with a 0.85 numerical aperture standard objective based on this method. The versatility of this approach has been demonstrated by imaging integrated chips, Blu-ray DVDs, biological cells, and various subwavelength 2D patterns, with a viewing area of up to 1000 µm^{2}, which is one order of magnitude larger than the previous far-field and full-field nanoscopy methods. This new resolving technique is label-free, is conveniently integrated with conventional microscopes, and can potentially become an important tool in cellular biology, the on-chip industry, as well as other fields requiring wide-field nanoscale visualization.

Design of hybrid structure for fast and deep surface plasmon polariton modulation.

The electric and optical performance of different surface plasmon polariton (SPP) electric modulation structures have been investigated by comparing the response speed and modulation figures of merit (FoM). To overcome the capacitance limitation and improve the response speed, we proposed a novel silver-graphene-dielectric-graphene-semiconductor vertical structure. Semiconductor nano-waveguide is introduced to help reduce ohmic loss in silver waveguide and reflect the leaked optical field back, enhancing the modulation depth. Through optimization, a device with estimated modulation FoM of more than 70% and hundreds of GHz response speed and 3 dB bandwidth is designed, which may bring great improvement to previous optical modulators.

High-Refractive-Index Chip with Periodically Fine-Tuning Gratings for Tunable Virtual-Wavevector Spatial Frequency Shift Universal Super-Resolution Imaging.

Continued research in fields such as materials science and biomedicine requires the development of a super-resolution imaging technique with a large field of view (FOV) and deep subwavelength resolution that is compatible with both fluorescent and nonfluorescent samples. Existing on-chip super-resolution methods exclusively focus on either fluorescent or nonfluorescent imaging, and, as such, there is an urgent requirement for a more general technique that is capable of both modes of imaging. In this study, to realize labeled and label-free super-resolution imaging on a single scalable photonic chip, a universal super-resolution imaging method based on the tunable virtual-wavevector spatial frequency shift (TVSFS) principle is introduced. Using this principle, imaging resolution can be improved more than threefold over the diffraction limit of a linear optical system. Here, diffractive units are fabricated on the chip's surface to provide wavevector-variable evanescent wave illumination, enabling tunable spatial frequency shifts in the Fourier space. A large FOV and resolutions of λ/4.7 and λ/7.1 were achieved for label-free and fluorescently labeled samples using a gallium phosphide (GaP) chip. With its large FOV, compatibility with different imaging modes, and monolithic integration, the proposed TVSFS chip may advance fields such as cell engineering, precision industry inspection, and chemical research.

Fiber-Integrated Reversibly Wavelength-Tunable Nanowire Laser Based on Nanocavity Mode Coupling.

As an ideal miniaturized light source, wavelength-tunable nanolasers capable of emitting a wide spectrum stimulate intense interests for on-chip optoelectronics, optical communications, and spectroscopy. However, realization of such devices remains a major challenge because of extreme difficulties in achieving continuously reversibly tunable gain media and high quality (Q)-factor resonators on the nanoscale simultaneously. Here, exploiting single bandgap-graded CdSSe NWs and a Fabry-Pérot/whispering gallery mode (FP/WGM) coupling cavity, a free-standing fiber-integrated reversibly wavelength-tunable nanolaser covering a 42 nm wide spectrum at room temperature with high stability and reproducibility is demonstrated. In addition, a 1.13 nm tuning spectral resolution is realized. The substrate-free device design enables integration in optical fiber communications and information. With reversible and wide, continuous tunability of emission color and precise control per step, our work demonstrates a general approach to nanocavity coupling affording high Q-factors, enabling an ideal miniaturized module for a broad range of applications in optics and optoelectronics, with optical fiber integration.

Fast response CdS-CdSxTe1-x-CdTe core-shell nanobelt photodetector.

Quasi-one-dimensional semiconductor nanostructure-based photodetectors show high sensitivity but suffer from slow response speed due to surface reaction. Here, we report a fast-response CdS-CdSxTe1-x-CdTe core-shell nanobelt photodetector with a rise time of 11 µs, which is the fastest among CdS based photodetectors reported previously. The improved response speed is ascribed to the suppressed possibilities of surface reaction resulting from the core-shell structure and heterojunction among the CdS, CdSxTe1-x and CdTe. The measured response spectrum of CdS-CdSxTe1-x-CdTe core-shell nanobelt photodetector covers a wide range from 355 to 785 nm. Moreover, high responsivity (1,520 A/W) and large 3 dB bandwidth (∼22.9 kHz) are obtained along with the fast response. The high performance in responsivity, sensitivity, spectral response and photoresponse speed makes this device a promising candidate for practical application in optical sensing, communication and imaging.