A metallic microcones array-based plasmonic strcture is presented as an example for the purpose of experimentally exploring the dependence of ambient temperature and incident angle on resonance and absorption properties. The microcones array is fabricated using the technique of heavy ion tracking. The technique has advantages of large-area patterning, high-aspect ratio of unit dimension, controllable length, and multichoice of materials. Fabrication steps, mathematical fitting, and experimental measurements of optical absorption spectra are presented. To analyze the experimental data regarding thetemperature-dependence effect, a theoretical formula, a quasi-Gauss model, is applied to describe the relationship between temperature (T) and plasmonic wavelength (λSP). Our experimental results demonstrate that the variation of temperature and incident angle strongly affect the sensitivity of λSP and its absorption properties. Our experimental results indicate that this structure is capbale of acting as an optical sensor for detection of temperature and angular denpendence.
KEYWORDS: 3D image processing, 3D acquisition, Image processing, Microlens array, Cameras, Microlens, Imaging technologies, Imaging systems, 3D modeling, 3D applications
The traditional imaging method can only obtain the two-dimensional information of the object space in lateral resolution through a single exposure, but cannot obtain the longitudinal depth information. The depth information of the object space will be lost because the object cannot be reconstructed in three dimensions. The light field imaging technology enables reconstruction of three-dimensional objects by means of adding microlens arrays into a conventional camera system. The technology has a wide range of applications in medical, military, and entertainment. In this paper, a light field acquisition technology using microlens based on 3ds Max is proposed. A 3D object model was established using 3ds Max. By establishing a virtual microlens array, the crosstalk-free, high resolution and fast acquisition of the light field image by the microlens can be realized. Simulation study of the light field imaging technology can provide a highefficiency computational study. The acquired images are processed to reconstruct images from different perspectives. Finally, the light field imaging experiments based on microlens arrays is carried out to realize the image reconstruction in different perspective images. Reliability of the algorithm is verified.
In this paper, quite effective method for the design of phase-only and quantized diffractive optical element (DOE) for beam splitting with simulated annealing algorithm (SA) is presented. For this method employs the character that periodic DOE could generate periodic point array, design time and number of sampling point of DOE could be greatly reduced. Besides, the relation of the DOE parameters including the sampling size, number of sampling point and divergence angle are analyzed. The cause and elimination of the high diffraction orders is also investigated. Design result shows that our method is quite effective and can keep the higher diffraction efficiency and lower uniformity error compared to the Gerchberg-Saxton algorithm (GS).
A new type of structure which is composed of a Gaussian profile-shaped metallic nanograting, was put forth from the nanofabrication point of view. Dependence of the structural parameters on the sensitivity was analyzed by means of a multiple multipole program (MMP) method. One of the important applications of the nanograting is in biosensing: immunoassay. Our numerical simulation results showed that the sensitivity to refractive index of 490 nm/RIU and the reflection spectra at site of full-width at halfmaximum (FWHM) ~9 nm can be obtained through the optimized structure. The figure of merit (FOM) of the sensor can exceed 55. The resonant wavelength increases linearly with increasing of the refractive index of bio-samples. These reflection properties make the nanograting more suitable to be used in the localized surface plasma resonance (LSPR)-based biosensors for immunoassay.
An optical probe with a single aperture flanked by depth-tuned grooves is presented. It is employed as an example to investigate propagation properties of the plasmonic nanostructures with a nonparaxial Gaussian beam illumination. The propagation through the subwavelength aperture is the process that a near-field diffraction of the Gaussian beam interferes with the surface plasmon polaritons (SPP) wave induced wavelets on surface of the grooves. An enhanced optical transmission at the exit side of a subwavelength aperture and a degraded reflection at top side of the compound dielectric/metal nanostructure (air/glass/C/Ag/air) of the probe can be generated with this illumination. Characteristics of the Gaussian beam illumination have been studied numerically via analysis of the transmission and reflection issues. In contrast, the results for plane wave illumination were given as well. Two-dimensional (2D) finite-difference time-domain (FDTD) algorithm is employed for the 2D simulation.
Design of an enhanced surface plasmon polaritons (SPPs)–based nanostructure for the purpose of beam shaping is discussed. An indentation with depth-tuned grooves is presented to realize the beam shaping and extraordinary transmission. The nanostructure is directly fabricated using focused ion beam (FIB) milling on an Ag thin film coated on quartz with a thickness of 200 nm. A large measurement error is found during geometrical characterization of the nanostructures by use of an atomic force microscope (AFM) working in tapping mode. Apex wearing and 34 deg full cone angle of the probe generate the measurement errors during the characterization of nanostructures with a feature size of 200 nm and below. To solve this problem, an FIB trimmed AFM probe is employed in the geometrical characterization. The results show that the error is improved greatly using the trimmed probe. The desired excitation of the SPPs is derived using an optical fiber coupled CCD spectrometer after the modified geometrical characterization. The designed structure can be used as an optical probe for future inspection and detection use.
A new fabrication approach, virtual gray-scale mask via focused ion beam (FIB) direct milling for fabrication of micro-optical elements (MOEs), is introduced. The designed MOEs, e.g., micro-diffractive lenses with continuous relief and micro-gratings, are directly milled by the FIB by means of the method of the virtual gray-scale mask with ion energy and ion beam current of 30 keV and 3 nA, respectively. The method has a one-step fabrication process and is free of user computer programming for the one-step direct writing. It is a useful approach for those FIB machines without the user programming function. It will be helpful for integration of MOEs with top-end optical fibers for applications of miniaturization of spectrometers, optical fiber sensors, and micro-optical systems in biochemistry analysis use.
Metallic nano-slits film is proposed to implement beam manipulation, such as focusing, deflecting and imaging etc. The principle of this novel nano metric device, termed as plasmonic nano lens, is based on the different phase retardation of light when transmitted through a metallic film with arrayed nano-slits, which have constant depth but variant widths. The slits transport electro-magnetic energy in the form of surface plasmon polaritons (SPPs) in nanometric waveguides and provide desired phase retardations of beam manipulating with variant phase propagation constant. Numerical simulations of illustrative examples are performed through finite-difference time-domain (FDTD) method and show its validity as a lens and other potential photonic devices. In addition, extraordinary optical transmission of SPPs through sub-wavelength metallic slits is observed in the simulation and implies higher efficiency than usual binary devices featured with transparent and opaque regions.
In this paper, we discussed the beam focusing of light emerged from a subwavlength metallic slit surrounded by a set of grooves with constant space and width but variant depth at the exit side surface. Based on the numerical model presented by L. Martin-Moreno, F. J. Garcia-Vidal etc. (published in PRL 167401), we attempted to optimize grooves depth to obtain general beam manipulation, such as beam focusing. This attempt did not prove successful for many cases with variant focal length in our optimization practice, although some specific results display agreeable beam focusing with elongated focal depth. Further numerical computation shows that the excited electromagnetic field intensity around groove openings has a strong dependence on the groove depth, but the phase only vary with a maximum change value of π by tuning the groove depth. This property restricts greatly the modulation of electromagnetic field by just changing each groove depth. More geometrical parameters, including groove space and width, are recommended for optimization in the design of nano metallic groove and slit structures for specific beam manipulation.
Integration of micro-optical elements (MOEs) with optical fiber at top-end was realized by use of focused ion beam (FIB) direct milling. The designed MOEs (micro-refractive lens, micro-diffractive lens with continuous relief, and micro-gratings) were directly milled by the FIB with ion energy and ion beam current of 40 keV and 569 pA, respectively, in the core area of both single mode fiber and multimode finer for dispersion and focusing uses. The integrated fibers can be used in microspectrometer, optical fiber sensors, and micro-optical systems for biochemistry analysis.
It has been proved that NiTi shape memory alloy thin film is the best one for micro actuators as compared with the others, e.g., electrostatic, electromagnetic and piezoelectric thin films. If the deposition of NiTi thin films on silicon wafers is carried out at room temperature, the resultant thin films are normally amorphous without shape memory. Subsequent annealing in a high vacuum chamber is required for re-crystallization. In this paper, we present an alternative annealing approach, namely by CO2 laser. After laser annealing, optical microscope, X-ray diffraction (XRD) and atomic force microscope (AFM) were applied to characterize the NiTi thin films. Strong austenite/martensite lattice structures were observed by XRD. The relationship between the surface roughness of the annealed NiTi thin film and temperature was obtained using AFM. The results indicate that the CO2 laser annealed NiTi thin films are with shape memory.
The wave shape of CCD output signal, on the one hand, reflect the result of synthetic influence between CCD itself and the parts before it. On the other hand, it reflects the degree of difficulty to derive and process signals for the circuits after it. Thus, relative factors affecting measurement accuracy can be known by analyzing the CCD wave shape. This analysis not only built the foundation for measuring total error of the system, but also obtained some important designing parameters. Basis can be provided for definite relative parameters in the case of whole system designing. It can be known from the analysis that slope of the wave shape and its amplitude difference (Delta) Vs directly influence deriving the CCD signal. It also affect the measurement accuracy of the system. (Delta) Vs also relates to the number of photoelements m passed by image during the period of CCD photo-integral.
Fabrication errors and its affecting factors were analyzed for multilevel DOE in this paper. A method of Moire fringe alignment was put forth. It was proved by actual manufacturing that this way is available for aligning positioning error.
The method of proximity photolithography is a practical and available way in the manufacture of gratin and radial encode. One of the most important factors of this way is lithographic gap. That is the distance from mask to surface of photoresist coated on ruled blank. The size of it affects the ruling quality directly, such as causing edge scattering. Because of the existing near-field Fresnel diffraction, it is impossible to obtain the ruling which is the same as the mask even if on the first focal plane of Fresnel. As it is very difficult to produce the exact parallel light in usual optical system, the actual image we get is not an ideal self-image. Therefore, a better position of the mask should be found in order to ensure the ruling quality. The relationship between image contrast and lithographic gap is deduced in the view of image contrast in this paper. According to the relation, rang of practical lithographic gap is obtained. Thus, a reliable basis is provided for selecting the best gap in actual photolithography.
The calculation formula of the far-field diffraction pattern for mm-wave diffraction antenna with a continuous phase structure is derived by current-distribution method. The simulation calculation using this method is compared with the experiment results for a diffraction antenna prototype operating at 8 mm wavelength. The simulation results coincide well with the measured data.
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