Showing 3 results for Frequency Domain
M. Pourmahyabadi, Sh. Mohammad Nejad,
Volume 5, Issue 3 (9-2009)
Abstract
In this article, perfectly matched layer (PML) for the boundary treatment and an efficient compact two dimensional finite-difference frequency-domain (2-D FDFD) method were combined to model photonic crystal fibers (PCF). For photonic crystal fibers, if we assume that the propagation constant along the propagation direction is fixed, three-dimensional hybrid guided modes can be calculated by using only a two-dimensional mesh. An index-guiding PCF with an array of air-holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs). Using this model, the fundamental characteristics of single mode photonic crystal fibers (SMPCFs) such as confinement loss, bending loss, effective mode area and chromatic dispersion are numerically investigated. The results revealed that low confinement loss and zero-flattened chromatic dispersion can be obtained by varying the air-holes diameter of each ring along the PCF radius. In this work, an especial PCF with nearly zero-flattened dispersion (1.3 ps/nm/km) over a wide wavelength range which covers O, E, S, C, L and U telecommunication wavelength bands and low confinement loss (0.06 dB/km at 1.55μm) is designed. Macro-bending loss performance of the designed PCF is also studied and it is found that the fiber shows low bending losses for the smallest feasible bending radius of 5 mm. Also, it is revealed that the temperature sensitivity of PCFs is very low in compared with the conventional fibers.
M. Aliramezani, Sh. Mohammad Nejad,
Volume 8, Issue 2 (6-2012)
Abstract
In this paper, a novel design of all-solid photonic bandgap fiber with ultra-low
confinement loss is proposed. The confinement loss is reduced remarkably by managing the
number of rods rings, up-doping level, pitch value, and rods diameters. Moreover, the
designed PCF shows ultra-flattened dispersion in L- and U-band. Furthermore, a new
design, based on introducing of an extra ring of air holes on the outside of the all-solid
bandgap structure, is then proposed and characterized. We demonstrate that it significantly
reduces the fiber diameter to achieve negligible confinement loss. The validation of the
proposed design is carried out by employing a two dimensional finite difference frequency
domain with perfectly matched layers.
Z. Shokhmzan, M. R. Mosavi, M. Moazedi,
Volume 13, Issue 4 (12-2017)
Abstract
The vulnerability of civil GPS receiver to interference may be intentional or unintentional. Among all types of interference, replay attack intended as the most dangerous intentional one. The signal structure of replay attack is almost the same with the satellite signal. The interference effects can be reduce with the design of an appropriate filter in the receiver. This paper presents two methods based on Finite Impulse Response (FIR) filter in frequency and time domain to mitigate the interference effect on GPS signals. Designed FIR filter protects GPS against the replay attack. The suggested filter is applied in the acquisition of the receiver. The proposed method has been implemented on collected dataset. The results show that the proposed algorithms significantly reduce interference. Also, they improve Position Dilution of Precision (PDOP) parameter. Based on the results, the FIR filter technique in time domain has better performance than the frequency domain.
