With study on the switching characteristics in a asymmetric dual-core nonlinear fiber coupler, it is found the switch efficiencies when the dispersion values of two fibers have opposite signs are much higher than those when they have same signs. Meanwhile, when the dispersion values of two fibers have same signs, the switch efficiencies become much higher if the dispersion value of one core is decreased. In addition, the switch threshold power becomes lower than the one with the same sign if the nonlinearity coefficient of two fibers is opposite. The result shows that asymmetric coupler has much higher switch efficiencies and lower switch threshold power than symmetric coupler. 相似文献
We report the observation of degenerate four-wave mixing in InSb at 5 K using a cw CO laser operating in the spectral region just below the bandgap energy, where strong self-defocusing and optical bistability have previously been seen. Conversion efficiencies of ≈1% are obtained with <13 mW beam powers, and higher efficiencies are predicted for improved phase-matching. 相似文献
Solid‐state lighting (SSL) is now the most efficient source of high color quality white light ever created. Nevertheless, the blue InGaN light‐emitting diodes (LEDs) that are the light engine of SSL still have significant performance limitations. Foremost among these is the decrease in efficiency at high input current densities widely known as “efficiency droop.” Efficiency droop limits input power densities, contrary to the desire to produce more photons per unit LED chip area and to make SSL more affordable. Pending a solution to efficiency droop, an alternative device could be a blue laser diode (LD). LDs, operated in stimulated emission, can have high efficiencies at much higher input power densities than LEDs can. In this article, LEDs and LDs for future SSL are explored by comparing: their current state‐of‐the‐art input‐power‐density‐dependent power‐conversion efficiencies; potential improvements both in their peak power‐conversion efficiencies and in the input power densities at which those efficiencies peak; and their economics for practical SSL. 相似文献
III‐nitride light‐emitting diodes (LEDs) and laser diodes (LDs) are ultimately limited in performance due to parasitic Auger recombination. For LEDs, the consequences are poor efficiencies at high current densities; for LDs, the consequences are high thresholds and limited efficiencies. Here, we present arguments for III‐nitride quantum dots (QDs) as active regions for both LEDs and LDs, to circumvent Auger recombination and achieve efficiencies at higher current densities that are not possible with quantum wells. QD‐based LDs achieve gain and thresholds at lower carrier densities before Auger recombination becomes appreciable. QD‐based LEDs achieve higher efficiencies at higher currents because of higher spontaneous emission rates and reduced Auger recombination. The technical challenge is to control the size distribution and volume of the QDs to realize these benefits. If constructed properly, III‐nitride light‐emitting devices with QD active regions have the potential to outperform quantum well light‐emitting devices, and enable an era of ultra‐efficient solid‐state lighting.
Basic thermofluid processes of a positive displacement compressor are strongly dependent upon the acoustic behavior of the manifolds. The tuning process of such a compressor is fairly complex as increases in the mass flow rate may not correspond with higher energy efficiencies. In this paper a computer simulation program is described, which includes the manifold back pressure effect, developed to investigate and explain the tuning phenomena for a single or two-cylinder reciprocating compressor. A symmetric suction manifold system for a two-cylinder refrigeration compressor has been considered as the example case in this tuning study. Results for flow efficiency, energy efficiency, and pressure pulsations at the valve exit are presented in terms of the acoustic natural frequencies of the manifold system. Predicted results compare reasonably well with experimental data. Based on this study, it is possible to choose optimal manifold dimensions which will provide higher efficiencies with lower pressure pulsations. 相似文献
Crossed laser molecular beam configuration was used to study the photoionization of U and UO by the UV-lines of an argon ion laser. Photoionization efficiencies of both U and UO were found to be line sensitive. Photoionization by the 3638 Å line was observed for the first time. Uranium atom ionization efficiency being higher for the 3345 Å and 3511 Å groups of lines, while UO ionization efficiency being maximum for the 3638 Å line. Dependence of photoion signal on laser power and relative photoionization efficiencies of the two isotopic species of uranium are also investigated. 相似文献
We present designs of high-efficiency compression grating based on total internal reflection (TIR) for picosecond pulse laser at 1053 nm. The setup is devised by directly etching gratings into the bottom side of a prism so that light can successfully enter (or exit) the compression grating. Dependence of the −1 order diffraction efficiencies on the constructive parameters is analyzed for TE- and TM-polarized incident light at Littrow angle by using Fourier modal method in order to obtain optimal grating structure. The electric field enhancement within the high-efficiency TIR gratings is regarded as another criterion to optimize the structure of the TIR gratings. With the criterion of high diffraction efficiency, low electric field enhancement and sufficient manufacturing latitude, TIR compression gratings with optimized constructive parameters are obtained for TE- and TM-polarized incident light, respectively. The grating for TE-polarized light exhibits diffraction efficiencies higher than 0.95 within 23 nm bandwidth and relatively low square of electric field enhancement ratio of 5.7. Regardless of the internal electric field enhancement, the grating for TM-polarized light provides diffraction efficiencies higher than 0.95 within 42 nm bandwidth. With compact structure, such TIR compression gratings made solely of fused silica should be of great interest for application to chirped pulse amplification (CPA) systems. 相似文献
In this paper, white light emitting diodes (LEDs) with good color rendering indices (CRI) and high luminous efficiencies have been fabricated by the encapsulation of mixed and double-deck phosphors. Experimental results revealed that white LEDs with the encapsulation of double-deck phosphors exhibited better CRI and higher luminous efficiencies than those with the encapsulation of mixed phosphors because no secondary excitation took place. The hue, CRI, and luminous efficiencies of white LEDs with double-deck phosphors under 200 mA were CIEx,y = (0.357, 0.348), 90, and 62.3 lm/W, respectively while the hue, CRI, and luminous efficiencies of white LEDs with mixed phosphors under 200 mA were CIEx,y = (0.366, 0.354), 89, and 56.5 lm/W, respectively. 相似文献
This paper reviews recent developments in the field of amorphous-silicon-based thin-film solar cells and discusses potentials
for further improvements. Creative efforts in materials research, device physics, and process engineering have led to highly
efficient solar cells based on amorphous hydrogenated silicon. Sophisticated multijunction solar cell designs make use of
its unique material properties and strongly suppress light induced degradation. Texture-etching of sputtered ZnO:Al films
is presented as a novel technique to design optimized light trapping schemes for silicon thin-film solar cells in both p-i-n
and n-i-p device structure. Necessary efforts will be discussed to close the efficiency gap between the highest stabilized
efficiencies demonstrated on lab scale and efficiencies achieved in production. In case of a-Si:H/a-Si:H stacked cells prepared
on glass substrates, significant reduction of process-related losses and the development of superior TCO substrates on large
areas promise distinctly higher module efficiencies. A discussion of future perspectives comprises the potential of new deposition
techniques and concepts combining the advantages of amorphous and crystalline silicon thin-film solar cells.
Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 14 June 1999 相似文献