The analysis of the diffractive phase elements (DPEs) that synthesizes pseudo-nondiffracting beams (PNDBs) in different axial regions are described. Those elements are designed by using conjugate-gradient method algorithm. To meet the requirement of lithography fabrication process, the obtained optimum continuous surface profile of DPEs must be quantized in the multilevel structure. In order to analyze the impact of different quantization levels, the axial-illuminance RMS variance of PNDBs for each quantized DPE is calculated and compared with each other. The compared results show that the axial illuminance of the PNDB of DPE with smaller-levels quantization fluctuates more rapidly than that of DPE with larger-levels quantization. Meanwhile, the analyses also show that the axial uniformity of the PNDB of DPE with a longer focal length is less sensitive to the quantization level.
A sandwich structure including subwavelength grating and low-index thin film as a broadband polarizing beam splitter
(BPBS) is demonstrated. The BPBS is studied by using the rigorous coupled-wave analysis (RCWA) numerical scheme.
The low-index thin-film with optimum thickness forms between the silicon substrate and the subwavelength grating.
While the thickness of low-index thin film is larger than 0.6 m, the reflectivity of TE wave is larger than 0.95 in the
wavelength region [1.29 m, 1.66 m] under the normal incidence. In this region, the reflectivity of TM wave is low.
Meanwhile, it is also found that while the thickness of low-index thin film rise to 0.9 m, the extinction ratio of TM
polarization is less than 0.047 in the wavelength region [1.35 m, 1.48 m]. Therefore, the designed sandwich structure
consisted of subwavelength grating, low-index thin film and silicon substrate can be used as broadband polarizing beam
splitter.
An approach using micro lens arrays to confine the cone angle of light source in a solar simulator has been proposed to
verify the Fresnel lens in a high concentration photovoltaic (HCPV) system. Compared with other three prior arts by the
computer simulation, the proposed method had the characteristics of the better approximation to the direct normal
insolation and the low cost. Also, to ensure the erection of the evaluation system, the tolerance of lens alignment has
been analyzed. The results showed that to maintain at least the 50% of the maximum luminous flux incident on the solar
cell, the transverse and longitudinal tolerances of ±1.4 mm and ±4 mm, respectively, were required.
Unlike the conventional light-emitting diode (LED) luminaire with a planar substrate and only the forward emission, the proposed LED luminaire with a curved ceramic substrate can perform both the forward and the backward emissions and inherits the merits of good heat-dissipation and low cost from the ceramic substrate. Assembled with the proper primary optics, an illustrated LED bulb has been designed, fabricated and measured. The measured luminous intensity of the LED bulb has shown the backward emission and designed distribution with the beam-angle of 133 deg. To broaden the application areas, such a LED bulb on a curved substrate has been modularized as a streetlight. The measured results of the proposed streetlight have shown that the beam angle of the luminous intensity and the luminaire efficiency are 132 deg and 86%, respectively. Meanwhile, its luminous characteristics also fit the Chinese standard for lighting design of urban roads.
Unlike the conventional LED luminary with a planar substrate and only the forward emission, the proposed LED
luminary with a curved ceramic substrate can perform both the forward and the backward emissions. Assembled with the
proper primary optics, an illustrated LED bulb has been designed, fabricated and measured. The measured luminous
intensity of the LED bulb has shown the backward emission and designed distribution with the beam-angle of 133°. To
broaden the application areas, such a LED bulb on a curved substrate has been modularized as a streetlight. The
measured results of the proposed streetlight have shown that the beam angle of the luminous intensity and the luminaire
efficiency are 132° and 86%, respectively. Meanwhile, its luminous characteristics also fit the standard for lighting
design of urban roads.asei.c
The wavelength-selection trapezoid gratings which can improve the infrared absorptance contrast are demonstrated. The
spectral absorptance of silicon trapezoid grating is studied by using the rigorous coupled-wave analysis (RCWA)
numerical scheme. The optical performance of the trapezoid gratings with different side-wall slopes on the groove ridge
is calculated and analyzed. According to the analyzed results, the side-wall slope of the trapezoid grating plays an
important role for enhancing the contrast of the infrared absorptance. It is found that the absorptance peak is located at
the wavelength of 7.0 μm, which is equal to the period of the trapezoid grating. The maximum spectral absorptance
contrast is given at the proper side-wall slope of groove ridge of the trapezoid gratings. The influences of the oblique
incident light are also analyzed. When the incident angle increases, the absorptance peak deviates from the original
location of the normal incident condition. The absorptance peak not only decreases its magnitude but also be split.
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