A comprehensive numerical tool has been developed for the evaluation of the performances of Radio over Fiber (RoF) links intended for wireless signal distribution.At the transmitter end an appropriate set of rate equations allows to model the optical source as a solitary laser or as an appropriately injection locked laser. The optical channel is modeled putting into account the combined effect of fiber dispersion, laser source non ideal performances (e.g. non-linear effects, frequency chirp), and quadratic detection of the receiving photodiode. The simulation model developed can be a useful tool at the design stage allowing a preliminary evaluation of the characteristics of real RoF links. 相似文献
We demonstrate a highly tunable deep notch filter realized in a liquid-crystal photonic-bandgap (LCPBG) fiber. The filter is realized without inducing a long-period grating in the fiber but simply by filling a solid-core photonic-crystal fiber with a liquid crystal and exploiting avoided crossings within the bandgap of the LCPBG fiber. The filter is demonstrated experimentally and investigated using numerical simulations. A high degree of tuning of the spectral position of the deep notch is also demonstrated. 相似文献
In this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and
discussed. The main objectives of the present study are: a) to investigate experimentally the effect of the boiling onset
on the evaporation rate of water droplets; b) to measure the evolution of the solid surface temperature during evaporation;
c) to examine the possibility of improving spray cooling efficiencies. The behavior of small water droplets (from 10 to 50 μl)
gently deposited on hot, non-porous surfaces is observed. The evaporation of multi-droplet arrays (50 and 100 μl) under the
same conditions of the single-droplet tests is analyzed. In particular, the conditions which determine the onset of nucleate
and film boiling are stressed out. In the experimental tests, the interaction of different materials with several multi-droplet
systems is monitored by infrared thermography. The spray cooling efficiency is related to the solid temperature decrease as
a function of the water mass flux. In the present study, the effect of varying the droplet volume and the mass flux is also
analyzed and discussed. The results on the droplets evaporation time and on the solid surface transient temperature distribution
are also compared with the data obtained by the same authors during the analysis of droplet evaporation in total absence of
nucleate and film boiling. In order to analyze the different behavior of the evaporating droplet as a function of the solid
surface thermal conductivity, evaporative transients on aluminum, stainless steel and macor (a glass-like, low-conductivity
material) are considered.
Received on 20 February 1998 相似文献
Liquid crystal photonic bandgap fibers form a versatile and robust platform for designing optical fiber devices, which are highly tunable and exhibit novel optical properties for manipulation of guided light. We present fiber devices for spectral filtering and polarization control/analysis. 相似文献
A novel configuration is proposed for an all-optical device performing two key functionalities in a communication network
based on wavelength-division-multiplexing (WDM): reconfigurable add/drop and wavelength shifting of single channels. The device
is based on guided second-order nonlinear interactions, such as sum-frequency generation and difference-frequency generation,
between the WDM channels and a suitable pump beam. A directional coupler and two parallel waveguides allow the spatial separation
between the main WDM signal and the dropped or wavelength-shifted channel for a subsequent routing in the desired path. A
first numerical simulation provided a cross-talk level in the dropped channel lower than -41 dB and a wavelength-shifting
range of more than 40 nm.
Received: 18 May 2001 / Published online: 30 October 2001 相似文献
The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid droplets. In particular, the study is focused on the non-intrusive measurement of the transient contact temperature between impinging droplets and hot solid surfaces.
An experimental apparatus was built and set up in order to approach the non-trivial problem of the measurement of a solid–liquid interface temperature after droplet impingement. The solid–liquid interface temperature was monitored from below through a transparent-to-infrared material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.
The paper reports the main results that have been collected to date, with particular regard to the approaches used to coat the transparent solid. Some considerations are also expressed about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements. 相似文献
Continous advances in material technology, in the field of integrated optics and optoelectronics, allow the realization of devices with geometries more and more compact and complex. Because of this trend, there is a parallel need for accurate fully numerical CAD tools. Among new ones, the FDTD method, already widely and successfully used for the characterization of microwave and millimeter-wave devices, is emerging in optics community because of its accuracy and versatility. However, in spite of the tremendous increase in computing power, the applicability of the method is still limited by the typical dimensions of optical structures. To overcome these limitations a specialized version of the FDTD algorithm for the rigorous analysis of 3D optical and optoelectronic devices is proposed and validated. This new technique is then used to characterize the optical behaviour of a MQW waveguide electroabsorption modulator. 相似文献
Microfluidic devices are used today in many engineering applications. However, despite much progress in this field, the fundamental understanding of fluid flow and heat transfer on the microscale is still not satisfactory. In this study, the rarefaction effects on the pressure drop for an incompressible flow through silicon microchannels having a rectangular, trapezoidal or double-trapezoidal cross-section are investigated. The roles of the Knudsen number and the cross-section aspect ratio in the friction factor reduction due to the rarefaction are pointed out. 相似文献