Optical Fibre Pulse Position Modulation Research Articles

Timing jitter and its impact on a self‐synchronised optical fibre PPM system

AbstractAn original spectral characterisation for the jitter in optical fibre pulse position modulation (PPM) is developed. The characterisation is used to examine the problem of slot synchronisation in PPM under two distinct cases. First when the PPM system is dominated by the self modulation noise namely the pattern‐dependent jitter. Then when both pattern and receiver‐generated jitter accumulate to impair the PPM system. We present a thorough performance analysis of the system under jitter impairment. Original results are obtained for the slot timing variance and the wrong slot error probability (WSE) in terms of the PPM number of slots, the phase lock loop (PLL) bandwidth and the normalised fibre bandwidth. The results indicate that with proper selection of the system parameters the slot jitter impairment can be minimised and maintained within prespecified levels. Frame synchronisation robustness is examined for a novel class of frame synchronisers previously proposed. Original results are presented for the extracted frame clock timing variance and the system WSE probability due to frame clock jitter when the system is dominated by its self noise. The frame synchronisers performance is shown to be optimisable through proper selection of the PLL bandwidth and the number of natural sequences tracked.

On the spectral estimation and synchronization of the cyclostationary optical fibre PPM process

Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB. >

Performance and optimal presynchronisation filtering for direct-detection optical fibre PPM

A thorough performance analysis is presented for a self-synchronised direct-detection optical fibre pulse position modulation (PPM) system. A new hybrid erbium-doped fibre amplifier (EDFA) PPM system is analysed. Sensitivity results are presented for a system operating at 622 Mbit/s and lambda =1.53 µm. These results indicate that EDFA PPM offers 7.9 dB sensitivity improvement over a comparable PCM system and is beyond the PCM fundamental limit. An original expression is presented for the PPM power spectral density under jitter. Original results are given for the extracted-slot clock timing variance and the resultant jitter wrong-slot error probability. The sensitivity penalty associated with self synchronisation is investigated and shown to vary between 0.15 and 1.9 dB for the range of parameters considered. An original presynchronisation filtering strategy is proposed and results are presented demonstrating its effect. The sensitivity penalty was bound to about 0.1 dB when the proposed presynchronisation filter was utilised.

Optimally filtered self-synchronized PPM PIN-BJT receivers

A common-collector common-emitter PIN-BJT receiver topology is considered for use with optical-fiber pulse position modulation (PPM). The PPM PIN-BJT system is shown to offer a sensitivity improvement of 8.6 dB over a comparable PCM system when both systems are operating at 140 Mbit/s and λ = 1.3 μm. The sensitivity penalty in self-synchronized PPM due to slot clock jitter is considered. This is shown to be significant (3.6 and 6.3 dB) at the set of parameters considered. An optimum presynchronization filter is derived and shown to result in the minimization of the jitter penalty. The inclusion of the filter resulted in reduction in the jitter penalty to about 0.1 dB for the two sets of parameters considered. © 1994 John Wiley & Sons, Inc.

Viability of optical fibre PPM soliton systems with Gordon-Haus effect reduction

The limit in transmission distance, associated with the Gordon-Haus timing jitter, is evaluated for an optical fibre pulse position modulation (PPM) soliton system employing a filter based Gordon-Haus effect suppression regime. It is demosntrated that while both PPM and PCM systems employing optical solitons benefit significantly from the introduction of the reduced Gordon-Haus regime the advantage PCM held over PPM for the unreduced Gordon-Haus limit is further extended.

Timing Considerations for Optical Fibre PPM

AbstractDigital pulse position modulation (PPM) has been shown to be an effective modulation format for the optical fibre channel. It is paricularly attractive as it can exploit the abundant mono‐mode optical fibre bandwidth to offer improved performance. The format is a discrete time modulation format wherein synchronisation at both the slot and the frame levels is vital. In this paper we derive an original analytic expression that predicts the spectral properties of optical fibre digital PPM on the basis of its cyclostationary random properties. We establish the conditions required to achieve both slot and frame synchronisation and further, we show that the system synchronisability can be optimised in terms of its parameters. In particular, we consider die effect of the pulse shape, modulation index and the data probability distribution on the spectral properties. Finally, we present original practical results measured on a 128‐ary PPM system and show that they are within 1 dB of those predicted by our analytic model. We conclude that optical fibre digital PPM synchronisation can be achieved and further, optimised, in terms of the major system parameters.