The principal factor in realising a high-performance bandwidth-efficient fibre communication system at an acceptable cost is the choice of modulation format on the optical carrier. In this context, pulse time modulation (PTM) techniques represent an attractive alternative to purely digital or analogue methods. The PTM family is reviewed, a classification system is proposed and their potential for use in high-speed fibre systems intended for the transmission of analogue data is examined.

Pulse time modulation techniques for optical communications: a review

Three methods to obtain compromised sets of excitations in monopulse antenna arrays are investigated. The techniques involve minimizing a scalar-valued performance measure, called cost function, via the use of simulated annealing method. The unknowns in the cost function are the weight factors of each sub-array or the relative amplitudes and the phases of the excitations of the array elements. Several examples are presented to illustrate the optimal results obtained.

Optimal compromise among sum and difference patterns

Lightwave-subcarrier-multiplexed (SCM) transmission systems can provide high-capacity and low-cost delivery of both current and future advanced TV signals. Compatibility of SCM technology with existing baseband digital transmission equipment would eliminate the need for a separate analog distribution network and thereby permit a more graceful evolution to a broadband integrated digital services network (B-ISDN). One version of a hybrid system whereby SCM video and baseband digital signals are simultaneously transmitted by a single laser diode, and the technical issues related to such an implementation are considered. An experiment is discussed in which the three color components of a high-definition TV (HDTV) signal and a baseband 622.08-Mb/s SONET STS-12 rate data signal are transmitted simultaneously by a DFB laser diode via frequency-modulated (FM) subcarriers, over 2 km of a single-mode fiber. >

A hybrid lightwave transmission system for subcarrier multiplexed video and digital B-ISDN services in the local loop

This paper introduces digital pulse interval modulation (DPIM), a new form of pulse time modulation format well-suited to use in free-space optical-links by virtue of its simplicity, increased transmission capacity and the absence of receiver synchronisation problems. Theoretical expressions are presented for transmission capacity, code characteristics and power spectral density, along with measurement from an experimental free-space prototype, showing the advantages of this new modulation scheme.

Digital pulse interval modulation for optical free space communication links

The derivation of a detailed expression for the frequency spectrum of pulse interval and width modulation (PIWM) is presented. Close agreement has been obtained between spectral predictions from the formula and experimental results. Design details and performance figures are also included for a practical PIWM optical fibre transmission link intended for use with TV, video and instrumentation signals.

Optical pulse interval and width modulation for analogue fibre communications

A design procedure has been developed to determine the required operating conditions for a pulse-frequency modulation (PFM) system (modulation index, required system bandwidth, and receiver carrier-to-noise ratio (CNR) for a specified receiver SNR (signal-to-noise ratio) and number of clicks per second. The PFM processing gain (=SNR/CNR) was measured to be 40 dB for a modulation index of beta =2.5, which agrees closely with the theory. The theoretical processing gain advantage of PFM over FM is 15.9 dB for a modulation index of beta =2.5 with receiver bandwidth B/sub rx/=50 MHz. >

H. Grebel

Papers

Video transmission in optical fiber communication systems using pulse frequency modulation