We investigate slow light effect of subwavelength gratings via Rayleigh Anomaly on both infinite and finite size high index contrast gratings. Our results show that the local group velocity of the transmitted light can be significantly reduced due to the optical vortex, which can inspire a new mechanism to enhance light-matter interactions for optical sensing and photo detection. However, the slow light effect will diminish as the transmitted light propagates further away from the grating surface, and the slow-down factor decreases as the grating size shrinks.
An Airy beam is a non-diffractive wave which propagates along a ballistic trajectory without any external force.
Although it is impossible to implement ideal Airy beams because they carry infinite power, so-called finite Airy beams
can be achieved by tailoring infinite side lobes with an aperture function and they have similar propagating
characteristics with those of ideal Airy beams. The finite Airy beam can be optically generated by several ways: the
optical Fourier transform system with imposing cubic phase to a broad Gaussian beam, nonlinear generation of Airy
beams, curved plasma channel generation, and electron beam generation. In this presentation, a holographic generation
of the finite Airy beams will be discussed. The finite Airy beams can be generated in virtue of holographic technique by
‘reading’ a hologram which is recorded by the interference between a finite Airy beam generated by the optical Fourier
transform and a reference plane wave. Moreover, this method can exploit the unique features of holography itself such as
successful reconstruction with the imperfect incidence of reference beam, reconstruction of phase-conjugated signal
beam, and multiplexing, which can shed more light on the characteristics of finite Airy beams. This method has an
advantage in that once holograms are recorded in the photopolymer, a bulky optics such as the SLM and lenses are not
necessary to generate Airy beams. In addition, multiple Airy beams can be stored and reconstructed simultaneously or
individually.
We propose a resonant optical Yagi-Uda nano-antenna fabricated at the end of the optical fiber probe for the sake of
extracting the information of the angular directivity by absorption of directional emission as a subwavelength optical
microscopy. A Yagi-Uda nano-antenna consists of a feed element surrounded by a reflector and three directors. The
reflector and directors are optimized in pitches with regards to resonance of the antenna elements using the finiteelement
method. We used a focused ion beam (FIB) to cut the end of the fiber probe tip away and make the flattened
surface to mount the metal nano-antenna structure, followed by FIB platinum deposition patterning for the nano-antenna.
To verify the characteristics of the probe based nano-antenna, directional emission from the metal slit with asymmetric
metallic surface gratings is probed and detected using the photomultiplier tube. Our approach of the nano-antenna based
fiber probe is suitable for scanning applications such as detection of directional emission.
We propose faced folded rods (FFR) as nano-antenna for light emissions. This FFR structure, which is composed of two
folded gold rods, shows two different field enhancement modes depending on the polarization direction of feeding light.
Under the incidence of x-polarized light, double hot spots are observed at gaps due to capacitive coupling between rods.
Meanwhile, when y-polarized light is applied to this geometry, a single hot spot is achieved at the center of the structure
which is due to the superposition of half-wavelength dipole resonance occurring at each folded rod. Strong resonance of
several vertices, which is predicted to be 100 of electric field enhancement factor in FFRs, can be achieved for sensitive
bio-molecular detection. Thus, we can manipulate the number and position of desired hot spots by way of controlling the
polarization state of light. Since we can obtain up to four different hot spot areas in nano-meter scale, multiplexed biosensing
can be possible using FFRs as the nano-antenna. To understand the physical mechanism behind the pair type of
folded rods, a single folded rod is first simulated as a basic elementary structure and compared with the pair structure.
Then, this FFR structure is fabricated with an electron beam evaporator and the focused ion beam lithography. The
scattered light intensity is captured by a CCD camera and compared with the simulation data.
In this work, an investigation on the condition of non-reflecting boundaries for the finite-embedded coordinate
transformed media will be present. Under the restriction that the mapping functions of coordinate transformed media are
defined in a concept of extended two-dimensional forms and that the incident waves are two-dimensionally propagating
fields, we examined the existence of the conditions for non-reflecting boundaries in a finite-embedded coordinate
transformed media. If we restrict the mapping functions of the coordinate transformation to the linear transformation, the
non-reflecting boundary condition can exist in two-dimensional transformations but not in the extended two-dimensional
cases. Both the numerical and analytical investigations are present.
Metamaterials can be classified into doubly negative materials and singly negative media according to their number of
negative constituent parameters. Contrary to the doubly negative media in which light can propagate just like in
dielectric layers, incident light to the singly negative materials cannot transmit through them. This opaque property,
however, can be overcome by using the interfaces between different kinds of singly negative media, i.e., permittivity-negative
and permeability-negative ones. In this paper, we investigate what kinds of surface-guiding modes such
interfaces can support and see what their unique features are.
We derive mathematical criteria for a pair of guided modes which have the same parity, mutually parallel wave vectors
along the guiding direction of the waveguide, but opposite directions of optical power flow in a negative-index slab
waveguide using a graphical method. It is also proven that the so-called light trap mode corresponds to the degenerate
mode of this pair. We also propose a waveguide structure in which guided light waves can be trapped via tunneling
through thin metamaterial clad layers. This trap is temporary since the trapped light tunnels out completely after a short time.
The hybrid integration of passive and optoelectronic devices has been widely researched. One of the main applications of this technique is for the fiber to the home (FTTH) network. In bi-directional transceivers, integrated WDM filters have been used to separate or combine the optical signals. Thin film filter (TFF) embedded waveguide type is effective for an application requiring wide bandwidth and low loss.
Although the insertion loss of TFF itself is quite low, significant loss occurs at the trench and it depends on the geometrical structure and fabrication errors of the trench waveguide. The conventional sawing method and deep reactive ion etching technique were used for trench fabrication. In the case of using DRIE process, fabrication error was reduced and position error of the trench was controlled within 1um. This method could also enhance the platform design flexibility. To reduce the coupling loss between input and reflection waveguides with high tolerance of filter position, a few mode waveguide and horn waveguide were proposed. The insertion losses of transmission and reflection were less than 0.5dB and 0.7dB respectively. The 1dB tolerance of filter position was improved to be nearly twice than that of the conventional waveguide.
We present experimental results showing the feasibility of parallel recording and reading of near-field holograms and also of fast data access time using a Si nanometric aperture array. We uses a Si(100) wafer and its anisotropic wet etching for the fabrication of nanometric aperture array. Then, this fabricated aperture array is applied to the storage and reading of binary near-field holograms using the near-field components generated at the aperture as object waves. A brief analysis on the amount of these evanescent components has been presented using the modified Bethe and Bouwkamp's formulation. Two near-field holograms are recorded in parallel and retrieved sequentially successfully with the array in contact with the surface of the photorefractive crystal, which shows the feasibility of parallel recording and reading of near-field holograms. The data access speed (reading speed) can be improved by more than 100 times compared with the case in which a fiber tip of the NSOM records and reads the near-field hologram.
KEYWORDS: Crystals, Refractive index, Near field scanning optical microscopy, Near field, Near field optics, Binary data, Laser crystals, Optical storage, Etching, Optical engineering
We suggest a way of photorefractive recording of sub- wavelength size optical information using the refractive index change induced by the single beam from the tapered fiber tip of the near-field scanning optical microscopy (NSOM). Data are recorded by the pure (without any change in the topography of the surface) refractive index change induced near the surface of photorefractive crystal by the light intensity distribution from the subwavelength-size fiber tip in NSOM. The size of index variation can be smaller than the size of wavelength since the distance between the tapered tip of NSOM and the crystal is about 10 nm. This can modify the transmission and collection characteristics of the light from the NSOM through the photorefractive crystal. Therefore, the characteristics of the reading beam depend on whether we previously exposed (recorded) the light from the tapered fiber tip or not and thus, the change in transmission or collection characteristics can be regarded as the on/off (binary) data.
KEYWORDS: Crystals, Near field, Near field scanning optical microscopy, Holograms, Multiplexing, Holography, Optical storage, Laser crystals, Near field optics, Semiconducting wafers
We present experimental results on the recording and retrieving multiplexed near-field holograms using near-field scanning optical microscopy (NSOM) and a conventional rectangular-parallelpiped or cubic photorefractive crystal. We use the fiber tip of NSOM both as an object and as a probe for scanning (reading) the images. The recording distance between the tapered tip of NSOM and the crystal (i.e. between the object and the recording medium) is a crucial factor determining the size of the stored spot and the angular selectivity since it is dependent on that distance whether the near-field components of the object wave can reach the crystal or not. Experiments on angular multiplexing show that the angular selectivity was about 0.01 degree and the retrieved spot size was smaller than the Rayleigh limit when the recording distance is about 10 nm. In addition, experiments show that near-fields originated from sub-diffraction-limit -size objects could be stored in a photorefractive crystal at 2 mm apart from the crystal surface resulting in the retrieval of sub-diffraction-limit- size spots which means that our scheme can provide a way of multilayer (stack-wise) near-field storage and, thus, contribute to the significant enhancement of the storage capacity of the near-field optical memory.
KEYWORDS: Holograms, Near field scanning optical microscopy, Multiplexing, Speckle pattern, Optical fibers, Holography, Multimode fibers, Speckle, Near field optics, Near field
Speckle patterns from optical fibers can be used as reference beams in holographic storage. Quasi-random patterns from multimode or tapered single mode fibers enhance hologram selectivity. The storage and retrieval of near-field photorefractive hologram using a near-field scanning optical microscope is also discussed.
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