Spider silks are expected to become biocompatible and bioresorbable optical fibers, which can be utilized to transfer localized optical energy for various biomedical applications such as optical therapy and optical imaging inside living tissue. In this study, the optical properties of eco-friendly native spider silk as an efficient optical fiber have been demonstrated experimentally. The metal shells on the surface of silk fibers are fabricated by using glancing angle deposition technique. Lightwaves with broadband wavelengths are coupled into the silk fibers by direct incorporation of conventional optical fibers. The measurement results show the transmission loss of approximately 2 dB/cm. The optical performances of silk-based core-shell fiber combine with the biocompatibility, bioresorbability, flexibility, and tensile strength. The silk-based core-shell fibers are capable of delivering optical power through biological tissue for biophotonic purposes.
We report on our recent approaches focused on the formation of a new class of subwavelength scale self-bending light beams, discovered in 2015, in application to in-plane surface plasmon. For the particle with broken symmetry (Janus particle) the morphology of the field localization area depends on the orientation of the particle that resembles the two faces of “Janus bifrons”. Photonic hook (PH) light do not propagate along straight line but instead follow curved trajectory. Wavefront analysis of such asymmetric mesoscale structure reveals that the unequal phase of the transmitted plane wave results in the irregularly concave deformation of the wavefront inside the structure that then leads to creation of the PH. Such dielectric structures enabling the realization of ultracompact wavelength-scaled and wavelength selective new inplane nanophotonic components.
In the past few years, it has shown that photonic jet – a high-intensity near-field focus can be curved through focusing of an asymmetric mesoscale dielectric particle. This unique electromagnetic beam configuration breaking spatial symmetry was termed ‘photonic hooks’ and demonstrated different features from Airy-family beams using a relatively simple experimental setup. The measured radius of the photonic curvature it creates approximates to half of the wavelength, which is the smallest curvature of electromagnetic wave ever reported. This effect was discovered in many relevant fields, including near-field optics (both in transmitted and reflection modes), terahertz (THz) radiation, in-plane plasmonics, and acoustics, and this paper is a short review for them.
We demonstrate the concept of fiber-based terahertz hook. The subwavelength photonic hook is obtained in the vicinity of a shaped fiber tip with asymmetric radiation. A 193 THz continuous-wave source, commonly used for medical imaging, has been required. Photonic hook with a lateral feature size less than the half-wavelength is achieved using a hemispherical shaped fiber tip with metallic mask. This breakthrough is carried out in ambient air by using a 2.58λ - diameter fiber with a shaped tip (λ is a radiation wavelength). A good correlation is observed between the computed intensity distribution of photonic hook and the tip sizes. Photonic hook generated with a shaped fiber tip, easier to manipulate, shows far-reaching benefits for potential applications such as ophthalmic laser surgery, super-resolution microscopy, photolithography, and material processing.
The generations of photonic jet array using rectangle phase diffraction grating at visible light region are demonstrated numerically and experimentally for the first time. The power flow patterns for the rectangle diffraction grating are simulated by using the finite-difference time-domain method. In experiment, the rectangle phase diffraction grating was fabricated with polydimethylsiloxane material. The direct imaging of the spatial and amplitude features for the gratingassisted photonic jet array is performed with a scanning optical microscope system. The focusing qualities of photonic jet array are evaluated in terms of focal length and transversal width along propagation and transversal directions. The photonic jet array could be operated in a wide range application for nanotechnology, self-assembly, energy generation and storage materials through the rectangle phase diffraction grating.
KEYWORDS: Visible radiation, Surface plasmon polaritons, Photon polarization, Range imaging, Photonic nanostructures, Diffraction gratings, Super resolution, Refractive index, Near field optics, Near field, Dielectrics, Finite-difference time-domain method, 3D modeling, Diffraction
The generations of localized photonic nanojets using core-shell diffraction gratings working in the visible light region are demonstrated numerically. The power flow patterns for the core-shell diffraction gratings are simulated by using the finite-difference time-domain method. The focusing qualities of localized photonic nanojets are evaluated in terms of focal length and transversal width along propagation and transversal directions. Due to surface plasmon polaritons, it has been demonstrated that the metallic shell is critical for power enhancement of photonic nanojet. The high-resolution imaging of the core-shell diffraction grating can be expected from the high-intensity photonic nanojet. The photonic nanojet could be operated in a wide range imaging for nano-scale targets through the core-shell diffraction grating.
The generation of linear photonic nanojet using core-shell optical microfiber is demonstrated numerically and experimentally in the visible light region. The power flow patterns for the core-shell optical microfiber are calculated by using the finite-difference time-domain method. The focusing properties of linear photonic nanojet are evaluated in terms of length and width along propagation and transversal directions. In experiment, the silica optical fiber is etched chemically down to 6 μm diameter and coated with metallic thin film by using glancing angle deposition. We show that the linear photonic nanojet is enhanced clearly by metallic shell due to surface plasmon polaritons. The large-area superresolution imaging can be performed by using a core-shell optical microfiber in the far-field system. The potential applications of this core-shell optical microfiber include micro-fluidics and nano-structure measurements.
Digital fringe projection techniques have been widely studied in industrial applications because of the advantages of high accuracy, fast acquisition and non-contact operation. In this study, a single-shot high-speed digital color fringe projection technique is proposed to measure three-dimensional (3-D) facial features. The light source used in the measurement system is structured light with color fringe patterns. A projector with digital light processing is used as light source to project color structured light onto face. The distorted fringe pattern image is captured by the 3-CCD color camera and encoded into red, green and blue channels. The phase-shifting algorithm and quality guided path unwrapping algorithm are used to calculate absolute phase map. The detecting angle of the color camera is adjusted by using a motorized stage. Finally, a complete 3-D facial feature is obtained by our technique. We have successfully achieved simultaneous 3-D phase acquisition, reconstruction and exhibition at a speed of 0.5 s. The experimental results may provide a novel, high accuracy and real-time 3-D shape measurement for facial recognition system.
The capability of generating photonic nanojets using dielectric cubes working in the visible light region is introduced and investigated numerically. The simulation of electric intensity distributions for a dielectric cube is performed using the finite-difference time-domain method. The focusing characteristic of the photonic nanojets is evaluated in terms of both focal length and transversal full width at half maximum along both transversal directions. Moreover, the ultra-long photonic nanojet is studied by theoretical calculations for a dielectric cube. By changing the dimension of the dielectric cube, it has been demonstrated that the focus point is moved from inside to outside the cube with a high intensity nanojet. The super resolution imaging of the dielectric cube can be expected from the focal length and the maximum intensity. The photonic nanojet enhancement and super resolution technique could be functional for the imaging of nanoscale targets on substrates and films.
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