We demonstrate two techniques to reduce the effects of fiber chromatic dispersion in fiber-wireless systems incorporating external modulators. We theoretically and experimentally show that the achievable link distance can be increased by varying the chirp parameter of the modulator to give large negative chirp using a dual-electrode Mach-Zehnder modulator (MZM) biased at quadrature. In addition, we show that dispersion can be almost totally overcome by implementing a simple method using the dual-electrode MZM to generate an optical carrier with single sideband (SSB) modulation. We demonstrate the transmission of a 51.8-Mb/s pseudorandom bit sequence (PRBS) at 12 GHz over 80 km of standard single-mode fiber using the SSB generator and measure a bit-error-rate (BER) power penalty due to fiber dispersion of less than 0.5 dB for a BER equal to 10/sup -9/.

Overcoming chromatic-dispersion effects in fiber-wireless systems incorporating external modulators

Hybrid fiber-wireless networks incorporating WDM technology for fixed wireless access operating in the sub-millimeter-wave and millimeter-wave (mm-wave) frequency regions are being actively pursued to provide untethered connectivity for ultrahigh bandwidth communications. The architecture of such radio networks requires a large number of antenna base-stations with high throughput to be deployed to maximize the geographical coverage with the main switching and routing functionalities located in a centralized location. The transportation of mm-wave wireless signals within the hybrid network is subject to several impairments including low opto-electronic conversion efficiency, fiber chromatic dispersion and also degradation due to nonlinearities along the link. One of the major technical challenges in implementing such networks lies in the mitigation of these various optical impairments that the wireless signals experience within the hybrid network. In this paper, we present an overview of different techniques to optically transport mm-wave wireless signals and to overcome impairments associated with the transport of the wireless signals. We also review the different designs of subsystems for integrating fiber-wireless technology onto existing optical infrastructure.

Fiber-Wireless Networks and Subsystem Technologies

The authors present a novel method for generating an optical carrier with single sideband modulation using a dual-electrode Mach-Zehnder modulator biased at quadrature. It is proposed and demonstrated experimentally that this simple technique can be used to reduce dispersion power penalties in fibre-radio systems.

Technique for optical ssb generation to overcome dispersion penalties in fibre-radio systems

Ultra-wide-band analog-to-digital (A/D) conversion is one of the most critical problems faced in communication, instrumentation, and radar systems. This paper presents a comprehensive analysis of the recently proposed time-stretched A/D converter. By reducing the signal bandwidth prior to digitization, this technique offers revolutionary enhancements in the performance of electronic converters. The paper starts with a fundamental-physics analysis of the time-wavelength transformation and the implication of time dilation on the signal-to-noise ratio. A detailed mathematical description of the time-stretch process is then constructed. It elucidates the influence of linear and nonlinear optical dispersion on the fidelity of the electrical signal. Design issues of a single-sideband time-stretch system, as they relate to broad-band operation, are examined. Problems arising from the nonuniform optical power spectral density are explained, and two methods for overcoming them are described. As proof of the concept, 120 GSa/s real-time digitization of a 20-GHz signal is demonstrated. Finally, design issues and performance features of a continuous-time time-stretch system are discussed.

Photonic time-stretched analog-to-digital converter: fundamental concepts and practical considerations

Dispersion causes a power penalty at certain fibre distances and frequencies in conventional millimetre-wave intensity modulation. Single sideband optical modulation at millimetre-wave frequencies using a fibre Bragg grating eliminates the dispersion-induced penalty over modulation frequency and fibre length.

Elimination of the fibre chromatic dispersion penalty on 1550 nm millimetre-wave optical transmission

A fiber chromatic dispersion compensation technique with optical single-sideband (SSB) transmission in optical homodyne detection systems is described. The chromatic dispersion compensation technique is demonstrated in a 6-Gb/s SSB phase-shift-keying (PSK) homodyne detection system equivalent experiment. A 270-km conventional single-mode fiber is used as a transmission medium at 1.55 mu m, and a microstrip line is used as a delay equalizer. The effect of compensating for the chromatic dispersion with the microstrip line is verified by improvement of eye-opening. >

N. Takachio

Papers

A fiber chromatic dispersion compensation technique with an optical SSB transmission in optical homodyne detection systems