Abstract
This paper presents an experimental investigation of sigma-delta modulation (SDM) as a means of improving the performance of underwater optical communication systems. The study considers the impact of the key parameters of SDM, including oversampling ratio, the system's signal-to-noise ratio, bandwidth, and optical link distance. The results of this study provide insights into the design and optimization of SDM-based underwater optical communication systems, paving the way for future research in this field. A fully digital solution, albeit operating at a lower bit rate than previously published OFDM counterparts, provides immunity against nonlinearities of the system and robustness to noise, which is relevant in harsh environments. Moreover, the proposed solution based on a first-order bandpass SDM architecture avoids the employment of a DAC at the receiver, simplifying its operation and reducing costs. An experimental investigation is carried out for the transmission of 16-QAM over SDM, and a transmission distance of 4.8 m over the underwater channel is achieved with a maximum transmission rate of 400 Mbit/s with an MER of 28 dB.

Abstract
We have investigated the possibility to erase arc-induced long period gratings through uniform exposure to UV-laser radiation and their potential recover by thermal annealing. The temperature stability of UV/arc-induced gratings is also presented. © 2000 Optical Society of America.

Abstract
A chirped fibre Bragg grating was written in an Erbium doped fibre. It was found that the slope of the reflected spectral power could be tuned by changing the pump power. The gratings fabricated were demonstrated to be useful in the development of a technique for optical interrogation of FBGs sensing heads with tunable sensitivity. © 2003 OSA/BGPP.

Abstract

Abstract

Abstract
In this paper, a new multiband antenna consisting of a coplanar patch antenna over an active artificial magnetic conductor (AMC) ground plane is demonstrated. The AMC ground plane, which has been proven to be very effective in the design of low profile antennas, consists of 4x4 square shaped unit cells. By connecting RF switches between adjacent unit cells, a group of four unit cells can be aggregated to a larger size unit cell. In this proposed antenna, the coplanar patch is placed 2mm above the AMC ground plane. It is observed that it is possible to use the patch to excite the AMC ground plane to become another resonant element. Moreover, operation in two more resonant frequencies can be achieved by reconfiguring the unit size of the AMC ground plane. In this way, one coplanar antenna can operate at four different bands with a simple configuration while keeping a low profile. In this work, it is shown that using the actively tuned AMC ground plane, one coplanar patch antenna can operate at 5.8GHz, 5.2GHz, 4.5GHz and 2.4GHz with a good operation bandwidth (S11<-10dB), which includes the entire required bands for WLAN 802.11a/b/g applications. The experimental and simulated results for impedance and radiation performance characterization are presented. All of the design and optimization work have been conducted using the Ansoft HFSS, which is a 3D full-wave electromagnetic field simulation software.