摘要:

The propagation constants of dielectric rib waveguides for optoelectronics are calculated by new methods designed either as an advance on typical existing methods, or for comparison with them. The classical variational methods agree with each other, but are somewhat pessimistic in that they underestimate the value of the propagation constant. Vector and scalar finite element or finite difference methods fall into a pattern of agreement with each other. Overall, there is a remarkable consensus between the values and the differences between them which highlights their advantages and disadvantages. The implications for directional couplers are briefly discussed.

DOI:10.1049/ip-j.1989.0018

出版商:IEE    

年代:1989

数据来源: IET

摘要:

We report changes in waveguiding characteristics of silver/sodium ion-exchanged optical waveguides after the post-baking treatment. The refractive index profile shapes of single-mode and multimode waveguides were investigated using the SEM method with a Robinson backscatter detector, while changes in waveguide attenuation was monitored using a 2-dimensional surface scattering system for various short and long postbaking times.

DOI:10.1049/ip-j.1989.0019

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A short analysis is presented for the quantitative estimate of the periodically varying photoconductivity, i.e. the longitudinal steady-state profile, in a semiconductor transmission line under multisection CW illumination. The analytical results demonstrate the dependence of photo-conductivity on the various parameters of the controlling light source, semiconductor material and transmission line structure.

DOI:10.1049/ip-j.1989.0020

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A nonlinear optical coupler can function as an optical transistor when operated near its critical power level. This analysis of the device includes high-order terms and gives suitable design ranges of the variables for practical use.

DOI:10.1049/ip-j.1989.0021

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A Gaussian approximation (GA) is commonly used to predict the performance of optical receivers. This is invariably the case if these incorporate superlattice avalanche photo-diodes (SAPDs) since a complete statistical description of the avalanche process associated with these advanced detectors has not been reported when residual hole ionisation is present. The objective of this paper is to present a more rigorous methodology for assessing the performance of these receivers thereby enabling a realistic assessment of the usefulness of the GA to be obtained. A numerical technique based on a discrete ionisation model is used to evaluate the gain moment generating function (MGF) for SAPDs taking into account the influence of both electron and hole ionisation. The MGF of the effective gain associated with detector dark current, generated in the various stages, is also determined using the same approach. This allows us to describe a flexible statistical model for the optical receiver, based on a modified Chenoff bound (MCB), to evaluate the performance of the detection process in the presence of hole ionisation, dark current, and circuit noise. The GA is investigated and compared with MCB calculations. The results indicate clearly that the GA, whilst slightly overestimating the receiver sensitivity (by less than 0.3 dB) and also overestimating the optimum gain, provides a generally good prediction of the opimum threshold and represents a useful basis for initial comparison of the performance of alternative receiver strategies.

DOI:10.1049/ip-j.1989.0022

出版商:IEE    

年代:1989

数据来源: IET

摘要:

For very high data rate optical communication systems, jitter is an impairment which may seriously degrade system performance. Previously reported methods for performance assessment of optical communication systems in the presence of jitter require the jitter probability distribution to be known. More commonly, only limited information is available, such as the measured jitter variance and the peak to peak range of the jitter. Assuming knowledge of the jitter statistics to be restricted to just the range and RMS value, we determine in this paper a new upper bound on the performance. For a certain class of signals, we derive a worst-case distribution (WCD) which consists of three Dirac impulses, located at the centre and at the extremes of the range. The usefulness of the WCD is demonstrated by means of examples which show that for many practical cases the new bound is tight. We show how the WCD may be combined with a modified Chernoff bound to obtain an overall upper bound on system performance which encompasses a comprehensive set of impairments including jitter. Since this requires only the range and RMS value of the jitter to be known, it provides a distribution free technique for assessing the influence of jitter on the performance of optical communication systems.

DOI:10.1049/ip-j.1989.0023

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A form of equaliser is derived which will optimally detect signals in a binary digital transmission system. It is shown to be a synthesis of the classic matched filter and transversal equaliser. Some results are presented for binary digital optical receivers comparing the optimum equaliser with the more common ‘raised cosine’ design. This latter approach is shown to be near optimum for the noise spectral characteristics encountered in optical receivers.

DOI:10.1049/ip-j.1989.0024

出版商:IEE    

年代:1989

数据来源: IET