In recent years, dielectric microspheres have been used in conjunction with optical microscopes to beat the diffraction limit and to obtain superresolution imaging. The use of microspheres on quantum dots (QDs) is investigated, for the first time, to enhance the light coupling efficiency. The enhancement of the QD luminescence collection in terms of extraction and directionality is demonstrated, as well as the enhancement of spatial resolution. In particular, it is found that a dielectric microsphere, placed on top of an epitaxial QD, increases the collected radiant energy by about a factor of 42, when a low numerical aperture objective is used. Moreover, if two or more QDs are present below the microsphere, the modification of the far field emission pattern allows selective collection of the luminescence from a single QD by simply changing the collection angle. Dielectric microspheres present a simple and efficient tool to improve the QD spectroscopy, and potentially QD-based devices. 相似文献
We report the enhancement of Raman scattering signal for the first time using photonic nanojet of a lollipop‐shaped microstructure (LMS) fabricated with the help of a nanosecond CO2 laser. The LMS consists of a dielectric microsphere attached to a long stem/tapered fiber. The enhancement was achieved by focusing the incident laser light on sample surface through the microsphere of LMS. The experimentally observed enhancement was found to be comparable with that obtained from commercial microspheres that are not attached to any stems. The value of enhancement was found to increase with the microsphere diameter. The dielectric stems/tapered fibers alone of the LMS are found not efficient for enhancing the Raman scattering signals. In contrast to the commercial microspheres, the fabricated LMSs are easy to handle, portable, and reusable. Also, unlike commercial microspheres, these LMSs allow the enhancement of Raman scattering without modifying the surface of substrates containing sample. Hence, these LMSs are extremely useful in the case of photonic nanojet‐mediated surface‐enhanced Raman scattering and fluorescence techniques for enhancing the Raman scattering and fluorescence signals of single/few molecules, respectively. 相似文献
We propose alignment-free optical modules using a solder-bump-bonding technique for constructing free-space optical interconnection
systems without a special alignment procedure. Bonding pads for mounting an optoelectronic device chip are fabricated by exposing
a photosensitive resin film to light traveling through the optical system of the module so that the image positions of the
bonding pads on both image planes of the optical interconnection system are aligned with each other. A device chip is mounted
by solder-bump bonding and is set at a proper position by the surface tension of molten solder. The effectiveness of the technique
is verified by constructing alignment-free optical modules. 相似文献
Epsilon‐near‐zero (ENZ) photonics is the study of light–matter interactions in the presence of structures with near‐zero permittivity and has been emerging as an important field of research in recent years. The introduction of zero permittivity structures also introduces a number of unique features to traditional photonic systems, including decoupling of their spatial and temporal field variations, tunneling through arbitrary channels, constant phase transmission, strong field confinement, and ultrafast phase transitions. Along with the continued developments in the theoretical research on ENZ photonics, many novel functional photonic devices are proposed and demonstrated experimentally, thus indicating the broad prospects of ENZ photonics for fabrication of high‐performance integrated photonic chips. Zero‐epsilon materials, which represent a singular point in optical materials, are expected to lead to remarkable developments in the fields of integrated photonic devices and optical interconnections. This review summarizes the underlying principles, the related novel physical effects, the fundamental principles for realization of ENZ photonic systems, and the integrated device applications of ENZ photonics. The review concludes with a brief overview of the challenges to be confronted and the potential development directions that may be pursued to realize extensive applications of ENZ photonics in the field of integrated photonic signal processing. 相似文献
From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology, and medicine. However, the extent of its practical realization relies on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom‐up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top‐down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or “digitally” has been heavily sought as it mimics the natural method of making matter and enables construction of nanomaterials with sophisticated architectures. An insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies, is provided. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing. 相似文献
A new method for enhancing the Raman scattering signal has emerged recently, based on dielectric enhancement. Especially promising is the dielectric method based on microspheres and photonic nanojet. In this paper, geometrical aspects and the influence of the incident beam parameters on Raman enhancement by silica microspheres were systematically investigated in three steps: by characterizing the incident beam using knife-edge method, performing horizontal and vertical Raman mapping imaging, and analyzing the results using ray transfer matrix analysis. Maps show a distinct enhancement (hotspot) area caused by the microsphere photonic nanojet and lens effect compared to a plain silicon substrate. Enhancement value on maps was the highest (5.7×) for 0.50 numerical aperture objective, when the incident beam size matched the microsphere diameter, and the focus of the incident beam was below the top of the sphere, so that the output beam focus was at the microsphere–substrate contact area. This geometrical configuration was confirmed as ideal by performing simple ray transfer matrix analysis. The ideal ranges of incident and output beam parameters match with the measured hotspot area. This three-step process and the usage of vertical Raman mapping have been, for the best of our knowledge, performed for the first time in such configuration. This research introduces a new way of investigating microsphere-assisted Raman enhancement, offers different approach to microsphere optics research, and improves current knowledge of the influence of the incident beam on the enhancement. 相似文献
By designing a microwave metamaterial with biaxial dielectric constants, a 2D polarization‐dependent effective gauge field is experimentally realized for electromagnetic waves. Such an effective gauge field is manifested by the oppositely shifted circular dispersions for two polarizations in k‐space. A polarization beam splitter is experimentally demonstrated as an immediate application of the effective gauge field. Rather than the conventional horizontal |H〉 and vertical |V〉 basis, it allows polarization beam splitting into the |H + V〉 and |H − V〉 basis in the transmission regime and works for a large span of incidence angles, and thus provides additional degrees of freedom in optical signal processing. The implementation has proved that biaxial dielectrics can be a straightforward approach to construct gauge‐field‐driven devices and the same design principle can be further extended to the optical regime. 相似文献
Subwavelength features in conjunction with light‐guiding structures have gained significant interest in recent decades due to their wide range of applications to particle and atom trapping. Lately, the focus of particle trapping has shifted from the microscale to the nanoscale. This few orders of magnitude change is driven, in part, by the needs of life scientists who wish to better manipulate smaller biological samples. Devices with subwavelength features are excellent platforms for shaping local electric fields for this purpose. A major factor that inhibits the manipulation of submicrometer particles is the diffraction‐limited spot size of free‐space laser beams. As a result, technologies that can circumvent this limit are highly desirable. This review covers some of the more significant advances in the field, from the earliest attempts at trapping using focused Gaussian beams, to more sophisticated hybrid plasmonic/metamaterial structures. In particular, examples of emerging optical trapping configurations are presented.
A hybrid conventional inverted/scanning near‐field optical microscope (Inverted/SNOM) has been obtained, by coupling an Olympus IX‐70 optical microscope with a SNOM head to combine the versatility and ease of use of the conventional microscope with the high‐resolution and three‐dimensional reconstruction obtainable with the SNOM technique. The head can be run in shear or tapping mode and is optimized to characterize soft, biological samples including living cells in physiological environment by including the SNOM in a cylindrical chamber that insulates it from the external noise, while maintaining a controlled temperature and atmosphere. Applications in the fields of biology and material science are presented. 相似文献
The properties of the photonic nanojet generated by a two-layer dielectric microsphere are studied. Simulation results indicate that this novel structure can generate a photonic nanojet outside its volume when the refractive index contrast relative to the background medium is higher than 2:1 in the condition of plane wave incidence. When the refractive index is smaller than 2, we show that an ultralong nanojet generated by the two-layer hemisphere has an extension of 28.2 wavelengths, and compared with the homogeneous dielectric hemisphere, it has superior performance in jet length and focal distance. Its dependence on the configuration and refractive index is investigated numerically. According to the simulation of the two-layer dielectric microsphere, a photonic nanojet with a full width at half maximum(FWHM) less than 1/2 wavelength is obtained and the tunable behaviors of the photonic nanojet are demonstrated by changing the reflective indices of the material or radius contrast ratio. 相似文献
