To investigate the impact of surface waves on the electromagnetic enhancement, here we consider a simple
geometry of a T-shaped metallic nano-groove that is composed of a narrow central groove and of a wide top
trench under illumination by a plane wave. The T-shaped groove is found to have a much higher enhancement
factor than a single bare groove without the top trench. By building up an intuitive surface-wave model, the
improved field enhancement is attributed to the surface waves that are collected by the top trench and are
coupled into the central groove.
From a microscopic point of view, we theoretically investigate fishnet metamaterials. We formulate the construction of
the fundamental Bloch mode by tracking the flows of energy through the fishnet structure. The analysis is supported by a
closed-form semi-analytical model based on surface-plasmon coupled-mode equations. The model provides an accurate
formula for the fishnet refractive index, including the real (negative-valued) and imaginary parts. The model simply
explains how the surface plasmon modes couple in the structure and it shines new light on the fishnet negative-index
paradigm at optical frequencies. It possesses broad flexibility in geometrical and material parameter tailoring of fishnet
properties, even including the gain-assisted case.
We propose quantitative investigations of the Fabry-Perot resonance condition for the field enhancement by an isolated
subwavelength metallic groove. The resonance condition is obtained from a simple Fabry-Perot model. Our calculations
show that the electric field near the groove mouth that contacts the specimen is drastically enhanced under the resonance
condition but is depressed out of the resonance condition. Giant electric-field enhancement can be obtained for narrow
groove, which reveals nearly 108 magnification of Raman signals. A weak dependence of the electromagnetic
enhancement on the metal type is presented and explained.
The influence of lateral pressure on the propagation constant of grapefruit microstructure optical fibers is theoretically
investigated using a full-vector finite element method in this paper. With the different direction of lateral pressure, the change of
the propagation constant of grapefruit microstructure optical fibers is different. At present, the report of this aspect has not
been found out. The research has great signification in microstructure fiber sensors especially multidimensional optical fiber
In this paper, a common pulse shaping system is used to compress a femtosecond optical pulse beyond the spectrum limit. An effective optimization method is proposed to design the spectrum filter. Numerical examples are presented to illustrate the validity of the proposed method.
As the size of diffracting structures with a diffractive optical elements is on the order of or less than the illumination
wavelength, it is necessary to use a rigorous electromagnetic theory of diffraction to accurately analyze its performance.
A rigorous electromagnetic analyse of two-dimensional diffractive microlenses is presented. Without paraxial
approximation, the focusing performance of diffractive microlenses with different f-number have been determined
including diffractive efficiency with different incidence polarizations (TE polarization and TM polarization), and
different profile structures (continuous profile, 8-level profile and 2-level profile) of mircolenses, respectively. Both
scalar and rigorous analyses are performed on all these diffractive microlenses.
Superresolution owns considerable significance in many cases, such as optical data storage, confocal scanning microscopy and laser lithography. Variation theory of functional is used in this paper for the discussion on the limits of optical superresolution. Globally optimal solutions can be obtained by this theory with the upper bound of the radiation flux through the input plane restricted.
Axially symmetrical diffractive phase planes (DPPs) are easily fabricated and have been used in a variety of applications, especially for realizing uniform loop focal spot with steep side, flat top, flat side lobe and high efficiency. A kind of hybrid design algorithm combined ST algorithm and input-output algorithm is introduced for axially symmetrical DPPs design to realize uniform loop focal spot. The computer simulation has shown that the algorithm is robust and convergent. The DPPs has been designed to product uniform loop focal spot with high diffractive efficiency of the energy inside the loop spot, high uniformity for both main lobe and side lobe (both more than 96%), and steep side simultaneously.
By using a diffractive optical element (DOE), a new method to generate dark hollow laser beam (DHLB) is presented in this paper. The optimization theories to design the DOE can obtain a globally optimal solution in an exact analytic form. The generated DHLB shows good performances for actual applications, which testifies the validity of this new method.
An aperiodic two-dimensional diffractive optical element (DOE) with subwavelength features as an uniform beam shaper which shapes an input laser beam into an uniform intensity distribution in an observation plane has been designed. A rigorous design method combined an iterative optimization algorithm with a rigorous electromagnetic computation -- the finite-difference time-domain (FDTD) method has been proposed. The design method and the FDTD method have been discussed in detail. The simulated results have shown that the DOE designed by this rigorous method can produce an uniform field distribution with flat-top, steep edge and low profile error in an observation plane.
A diffractive superresolution element placed at the exit pupil can effectively increase the resolving power of an optical system for optical data storage. The theory of linear programming is suggested in this paper to design the diffractive superresolution elements, which can get globally optimal solutions. Examples of design and some limits of optical superresolution are presented, and a comparison between the results for a uniform incident field and those for a Gaussian incident field is performed.
Sub-wavelength gratings could function as polarization components, such as wave-plates and polarized beam splitters. Furthermore, gratings in resonate regime could act as achromatic wave-plate. Here, an achromatic quarter-wave plate of a submicrometer grating with sinusoidal profile is designed based on diffractive optics. Rigorous coupled wave theory (RCWT) was used to analyze the subwavelength grating made on photo-resist in ambient air. Design of a broadband form-birefringent phase retarder for 400nm to 800nm visible region is discussed. A sinusoidal sub-wavelength grating with good properties was designed. Its phase retard maintains at about 90° and maximum deviation is about 15%, which approaches normal binary waveplate.
Though DVD becomes more and more popular, there are still millions of CD-R disk in using. The ability of reading both DVD and CD-R disk is necessary in compatible disk drive. Traditional optical pickup consists of different bulk components, which result in high cost, high difficulty in assembly and low reliability. Integration is a way to overcome these troubles. Based on planar optics, an integrated digital versatile disk (DVD)/compact disk recordable (CD-R) compatible optical pickup has been developed. In this device, the beams of two wavelengths follow different zigzag optical paths inside a few-mm thick glass substrate, which is used as a light guide. It is demonstrated that a beam combiner, a polarized beam splitter, a Fresnel prism, and a beam separator were integrated around a glass substrate, and such a planar optical pickup exhibited an excellent performance with high efficiency. It confirms that planar optics is an effective way to realize compatibility of DVD/CD-R.
Composite recording material was synthesized by hydrolysis and polycondensation of tetraethoxyorthosilicate and silane with photoinitiator added. With infrared spectral, the mechanism of response to light of the material was investigated. Vibrational spectroscopy is used to provide insight into the structure changes that occur when films are exposed with UV light. The decrease of absorption intensity in v(C = O) 1698 cm-1 and v(C = C) 1636 cm-1 bands reveal the polymerization in material after irradiation. Comparative experiments between two systems with mixed initiation and sole initiation are exported. UV spectra show that the transmittance of the sol-gel thin films drops down in a wavelength range of UV with addition of photoinitiator and irradiation. Developed in dilute base solution, micro-optical elements, such as gratings, were fabricated by contact copy with UV-exposure.