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

Progress in technology, theory and applications of high-frequency mode-locked diode lasers is reviewed. We present a systematic overview of a wealth of experimental and theoretical results and approaches reported recently in the field of physics, technology and applications of monolithic mode-locked laser diodes.

Monolithic and multi-gigahertz mode-locked semiconductor lasers: constructions, experiments, models and applications

We have studied RF transmission over various multimode fibers (MMFs) and a standard single-mode fiber, targeting picocellular networks for voice, data, and video applications. Bandwidth requirements of MMF links that are based on vertical-cavity surface-emitting laser (VCSEL) have been extensively studied. The performance of the radio-over-fiber link is assessed in terms of the error vector magnitude. Also conducted was a full system analysis, including the investigation of an achievable dynamic range and a noise figure for different low-cost architectures. This was compared to coax-based RF transmission. The IEEE 802.11 a/b/g standard, as well as other applications like radio frequency identification tracking, was considered. For experimental investigations, we have used both commercial wireless access points and a vector signal generator as a signal source, with two types of directly modulated VCSELs - 850-nm sources and 1310-nm high-speed uncooled single-mode AlGaInAs/InP VCSELs. A robust system performance was demonstrated in both 2.4- and 5-GHz RF bands, and record multimode and standard single-mode fiber transmission distances were achieved. A transponder design that can meet system requirements in terms of sensitivity ( 95 dBldrHz2/3) for a dual-band wireless LAN (WLAN) fiber-radio picocellular network was developed. A full 14-cell experimental WLAN system with cells of 4-m radius was implemented to study networking issues such as handoff and cochannel interference.

Radio Over Fiber for Picocellular Network Architectures

Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.

Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications

A hybrid wireless optical and radio frequency (RF) communication link utilizes parallel free-space optical and RF paths for transmitting data and control and status information. The optical link provides the primary path for the data, and the RF link provides a concurrent or backup path for the network data, as well as a reliable and primary path for the control and status information. When atmospheric conditions degrade the optical link to the point at which optical data transmission fails, the hybrid communication link switches to the RF link to maintain availability of data communications. The switch may occur automatically, based on an assessment of the quality of the optical signal communicated through the optical path.

Hybrid wireless optical and radio frequency communication link

We investigate the generation of signals using pulsed semiconductor lasers for application in millimeter-wave (mm-wave) wireless links. The generation of mm wave harmonic frequencies in both mode-locked and gain-switched lasers is considered and a method to generate mm-wave modulated optical signals with modulation depths approaching 100% is implemented. The technique uses optical filtering to select only two optical modes in the pulsed laser spectrum that beat together in a highspeed photodiode. The application of this method to the feeding of mm-wave wireless links incorporating microstrip patch antennas is demonstrated. These optically fed links have application in indoor wireless LAN's and optical fiber microcellular systems. >

Signal generation using pulsed semiconductor lasers for application in millimeter-wave wireless links

Very efficient ultrastable millimetre-wave signal generation using hybrid modelocking of a monolithic distributed Bragg reflector semiconductor laser is demonstrated for the first time. Unlike conventional hybrid modelocking methods, a low-power (-1 dBm) RF signal is applied to the saturable absorber section of the laser. The detected laser output gives a 34 GHz signal with phase noise >

Ultrastable millimetre-wave signal generation using hybrid modelocking of a monolithic DBR laser

We report a method that enables an external‐cavity semiconductor laser to be actively mode locked at multiples of the radio frequency (rf) drive frequency. The key to this method is the choice of the relationship between the external cavity resonance frequency and the rf drive frequency. The repetition rate of the output pulses is the lowest common multiple of the external cavity resonance frequency and the rf modulation frequency. The method has been demonstrated in a laser with a cavity resonance frequency of 1 GHz; 17 GHz pulse streams were generated using rf drive frequencies of 8.49 and 5.67 GHz.

Frequency multiplication in actively mode‐locked semiconductor lasers

We present a millimeter (mm)-wave fiber-wireless system suitable for the transport and distribution of broad-band signals. We show transmission over fiber and wireless distribution of subcarrier multiplexed amplitude-modulation vestigial-sideband (AM-VSB) video and a digital data stream at 37 GHz using optical carriers generated by a hybrid mode-locked laser (HMLL). We also present a simple model to characterize the effect of fiber chromatic dispersion on the transport of mm-wave modulated signals over fiber, and calculations show that by using an HMLL, broad-band signals can be transported successfully over fiber lengths greater than 150 km using subcarrier frequencies <1 GHz and more than 50 km for subcarrier frequencies <3 GHz.

37-GHz fiber-wireless system for distribution of broad-band signals

A detailed model is developed for analyzing fiber grating external cavity lasers for both static and small-signal modulation conditions The chip and package parasitics and leakage current induced distortion are included The composite system is solved analytically in the small-signal regime using a Volterra functional series expansion method As an application of the model, a thorough analysis of the appearance of nulls close to the harmonics of the cavity resonance frequency in the noise and modulation spectra is given We show that the appearance of these nulls can be explained using the interplay of amplitude and phase coupling between laser diode and external resonant cavity A signal flow graph approach is introduced which identifies methods of minimizing the nulls

Z. Ahmed

Papers

Signal generation using pulsed semiconductor lasers for application in millimeter-wave wireless links

Ultrastable millimetre-wave signal generation using hybrid modelocking of a monolithic DBR laser

Frequency multiplication in actively mode‐locked semiconductor lasers

37-GHz fiber-wireless system for distribution of broad-band signals

Modeling noise and modulation performance of fiber grating external cavity lasers