UWB system based on gain-switched laser

Simulation results based on an UltraWideBand (UWB) system employing a gain-switched laser are presented. 156 Mb/s data stream modulates the position of short electrical pulses, which are then used to gain-switch the laser. The output optical pulses are then transmitted over fiber to a Remote Antenna Unit (RAU), where the signal is detected and undergoes spectral shaping (according to UWB requirements). The resulting Pulse Position Modulated (PPM) electrical impulses are then converted to an amplitude-modulated signal and down-converted. Bit Error Rate measurements are carried out on a back-to-back system and a transmission link (over different lengths of fiber

Remote downconversion scheme for uplink configuration in radio/fiber systems

The authors present a novel technology for uplink transmission in radio over fiber (RoF) distribution systems. The technique employs remote downconversion of the uplink data to intermediate frequency (IF) in the base station (BS). The local oscillator (LO) signal for the downconversion is optically generated in the central station (CS) and sent to the BS via optical fiber. The IF uplink data is then modulated onto an optical carrier and sent to the CS, where the baseband conversion takes place. By employing this method of uplink connection simplicity and cost efficiency of the BS is achieved

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems

Adjacent channel interference due to wavelength drift of a tunable laser in base-band and subcarrier multiplexed system

In this paper, we examine the amplitude and the duration of a wavelength drift of the tunable lasers at the most crucial moment, which is the time after the wavelength switch and measure the impact of this drift on the performance of the DWDM system spaced by 12.5 GHz. The adjacent channel interference is examined for two cases: firstly when the TL is modulated with base-band (BB) data, secondly when subcarrier multiplexing (SCM) is use

Development of highly flexible broadband networks incorporating wavelength division multiplexing and sub-carrier division multiplexing in a hybrid radio/fiber distribution system

A radio over fiber distribution system incorporating both SCM and WDM technologies is presented. The SCM signal contains five 155 Mbit/s data channels, centered around 18.5 GHz with 450 MHz spacing. This signal is directly modulated onto three high-speed lasers with emission frequencies spaced by 50 GHz. Bragg filters are employed at the receiver base station in order both to demultiplex the required optical channel, and to ensure that the detected signal is single side band (in order to overcome dispersion limitations on the link). Our results show negligible degradation in system performance for the demultiplexing of the WDM signal compared with the back-to-back performance curves

Remote downconversion with wavelength reuse for the radio/fiber uplink connection

The authors present a novel technology for uplink transmission in radio-over-fiber distribution systems. The technique employs remote downconversion of the uplink data to intermediate frequency (IF) in the base station (BS). The local oscillator signal for the downconversion is optically generated in the central station (CS) and sent to the BS via optical fiber. The IF uplink data is then modulated onto an optical carrier, retrieved from the downlink signal, and sent to the CS, where the baseband conversion takes place. By employing this method of uplink connection, simplicity and cost efficiency of the BS is achieved

Improved performance of a hybrid radio/fiber system using a directly modulated laser transmitter with external injection

A directly modulated laser diode with external light injection is used to generate microwave optical signals for a hybrid radio/fiber system. The external light injection greatly enhances the frequency response of the laser, and thus, significantly improves the overall performance of the hybrid system. Experimental results show a 14-dB improvement in system performance for the externally injected laser in a hybrid radio/fiber communication link used for distributing 155-Mb/s data signal

Multiple RF carrier distribution in a hybrid radio/fiber system employing a self-pulsating laser diode transmitter

A self-pulsating laser diode is used to generate a multicarrier microwave optical signal for use in a hybrid radio/fiber system. The self-pulsation frequency of the laser is controlled by external light injection, and can be varied between 14-24 GHz. The hybrid radio/fiber system, employing the self-pulsation laser, is used to distribute two 155-Mb/s data signals on two radio frequency (RF) carriers (at 18.5 and 18.9 GHz). Experimental results show the overall system performance for both RF channels, and demonstrate that the performance is improved by around 17 dB compared with the case when the laser is used without external injection, and thus, does not self-pulsat

Effects of intermodulation distortion on the performance of a hybrid radio/fiber system employing a self-pulsating laser diode transmitter

A self-pulsating laser is used to generate a multicarrier (five radio frequency (RF) channels) microwave optical signal for use in a hybrid radio/fiber system. The self-pulsation is achieved by external light injection into the laser diode. By varying the RF channel spacing, we have been able to estimate the degradation in system performance due to intermodulation distortion (caused by the nonlinear dynamic response of the laser). The power penalty on the central RF channel is found to be 3.2 dB for operation at the RF band around the laser self-pulsation frequency of 18.5 GHz. We have also characterized the performance of the multicarrier hybrid radio/fiber system in the frequency band corresponding to the inherent relaxation frequency of the laser

Broadband access networks using hybrid radio/fiber systems

Developing broadband access networks is one of the most urgent needs in the telecommunications world. The wireless systems provide an efficient solution to address the requirements for last mile connectivity of data, Internet and voice services Radio systems using millimetre-wave frequencies can supply home users with capacities in the order of 50-200 Mbit/s Such bit rates allow the transmission of broadband applications including digital TV, video-on-demand etc In order to provide the massive capacities that are required for the distribution of such broadband data between Central Station and Base Stations, optical fiber can be employed The enormous transmission bandwidth and low loss of the fiber ensure that high capacity microwave signals can be encoded on an optical carrier and successfully transmitted from a Central to Base Station. The goal of this project was to develop and test a radio over fiber communication system This involved investigating the generation of microwave optical signals for transmission in optical fiber, followed by an examination of the effect of fiber propagation on the microwave optical signals