Stavros Iezekiel

Radio-over-fiber transport for the support of wireless broadband services [Invited]

Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

Orthogonal frequency-division multiplexing in wireless communication systems with multimode fiber feeds

The feasibility of using multimode fiber as an inexpensive cell feed in broad-band indoor picocellular systems is investigated in this paper. The performance of coded orthogonal frequency-division multiplexing (OFDM) for a variety of multimode fiber profiles, including stepped index and /spl alpha/-profile graded index fibers, is assessed. In addition to its ability to perform well in a frequency-selective multipath environment, OFDM is shown to offer good protection against the frequency selectivity of a dispersive multimode fiber. Data rates in excess of 100 Mb/s (without equalization) over a multimode fiber channel are possible, whereas they may be limited to some 20-30 Mb/s using conventional ASK modulation.

Nonlinear dynamics in directly modulated multiple-quantum-well laser diodes

A theoretical and experimental analysis of the nonlinear dynamics of Fabry-Perot (FP) and distributed feedback (DFB) multiple-quantum-well (MQW) laser diodes is presented. The analysis is performed under single-tone and two-tone direct modulation. In the FP laser, we observe period doubling and in the DFB laser both period doubling and period tripling are identified. Period doubling is found over a wide range of modulation frequencies in both lasers. The reason for this wide modulation frequency range is attributed to the large relaxation frequencies found in MQW laser diodes. The spontaneous emission factor is measured for both FP and DFB lasers. The dependencies of period doubling on output power and RF input power level are also analyzed. The nonlinear dynamics of the laser are found to be enhanced when modulated under two-tone modulation. Numerical simulations carried out show good agreement with the measured results.

Synthesis of all-optical microwave filters using Mach-Zehnder lattices

A synthesis algorithm which generates the set of coupling ratios required to produce a desired time-domain window response using an all-optical Mach-Zehnder lattice network Is presented. The analysis assumes incoherent interference of the lightwaves within the structure. The window coefficients are dictated by the coupling ratios of the couplers forming the lattice, leading to a simple structure comprising only passive components. Since its impulse response (IR) is finite, the filter will be stable, and the algorithm is capable of generating a wide range of responses In terms of their extinction ratios and passbands. The theory has been validated by experiment.

RF Engineering Meets Optoelectronics: Progress in Integrated Microwave Photonics

Integrated microwave photonics (IMWP) is concerned with applying integrated photonics technology to microwave photonic systems. It is one of the most active and exciting areas of current research and development in microwave photonics (MWP), building upon the impressive foundations of integrated photonics in various systems involving material platforms such as indium phosphide (InP) and silicon nitride (Si3N4). The aim of this article is to explain to the wider microwave engineering community the significance of the new field of IMWP and to describe how it may potentially be applied to improve the performance and capabilities of microwave and millimeter-wave (mmWave) systems. Just as the microwave monolithic integrated circuit (MMIC) has revolutionized active microwave circuits, IMWP is poised to open up new applications for microwave engineering that take advantage of the unique functionalities offered by photonics, especially with regard to its large bandwidth.

A balanced self-oscillating mixer

A balanced self-oscillating mixer is proposed. It consists of a pair of AlGaAs/GaAs 10×45 μm pHEMTs, oscillating at 7.53 GHz and uses the extended resonance effect. The circuit exhibits a conversion gain of 3.6 dB and reduces the second-order intermodulation products by 18.3 dB. The balanced nature of the oscillators also provides good LO to RF isolation of 40.5 dB when used as an upconverter. This approach relaxes the filtering requirements for generating single-sideband AM.

Scattering parameter characterization of microwave optoelectronic devices and fiber-optic networks

A microwave fiber-optic network analyzer test set is proposed that will allow the application of two-port calibration theory to the measurement of optical and optoelectronic components in high frequency fiber-optic links. Formulae for the optoelectronic calibration are presented. A unified approach to optical and optoelectronic two-port calibration theory is covered.<<ETX>>

All-optical microwave filter design employing a genetic algorithm

The problem of synthesizing all-optical networks for microwave frequency filtering applications is addressed. Analysis techniques are based upon established discrete time signal theory, but the assumption of incoherent optical interference restricts the time domain output to positive values, thus preventing the reliable application of traditional digital filter design methods. A new approach, based on the application of genetic algorithms, is described and demonstrated. Results show this to be a viable and rugged solution to the problem, which unlike previous approaches, produces filters that meet the design specifications in an optimal fashion.

Nonlinear circuit analysis of harmonic and intermodulation distortions in laser diodes under microwave direct modulation

A microwave nonlinear circuit analysis technique which can account for all known steady-state responses has been developed and applied to the large-signal characterization of directly modulation laser diodes. An equivalent circuit derived from the rate equations is used to model the laser diode. The proposed technique is based on a harmonic balance algorithm which represents two-tone inputs by describing frequencies. Second-harmonic and third-order intermodulation distortion results for a single-mode GaAlAs diode have been compared with corresponding measured data to validate the method. Aperiodic responses are detected by means of bifurcation theory prior to the harmonic balance analysis and are simulated in the time domain. Simulated results are shown to agree well with published measurements, and indicate the capability of using this approach for the computer-aided design of microwave fiber-optic transmitters. >

Orthogonal frequency division multiplexing in wireless communication systems with multimode fibre feeds

The feasibility of using multimode fibre as an inexpensive cell feed in broadband indoor picocellular systems is investigated. The performance of coded orthogonal frequency division multiplexing for a variety of multimode fibre profiles, including stepped index and /spl alpha/-profile graded index fibres is assessed. In addition to its ability to perform well in a frequency selective multipath environment, OFDM is shown to offer good protection against the frequency selectivity of a dispersive multimode fibre. Data-rates in excess of 100 Mb/s (without equalisation) over a multimode fibre channel are possible, whereas they may be limited to some 20-30 Mb/s using conventional ASK modulation.