摘要:

The question of performance evaluation in digital pulse position modulation (PPM) transmitted over slightly dispersive optical fibres and detected by avalanche photodiodes (APD) is considered. In view of numerical complexity implicit in exact average error probability evaluation, a bound on this probability is derived. Making use of this bound we conclude that optical fibre PPM receivers based on APDs offer some improvement over optical fibre PPM receivers based on PINFETs and a big improvement when compared with PCM receivers.

DOI:10.1049/ip-j.1986.0053

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The Shockley-Queisser detailed balance calculation of solar-cell behaviour is not quite exact, but if the correct expression is used in a straightforward way, then the dark current shows an unphysical infinity when the terminal voltage approaches the energy gap value from below. To eliminate this, it is necessary to allow for the reduction in optical absorption which occurs at the same time, turning to emission whenqV>Eg. If this is done, there is a reduction in photocurrent and an increase in dark current, however there is no discontinuity in behaviour whenqV=Eg. WhenqV>Eg, the lasing condition holds, so that the calculation shows clearly the transition of diode behaviour from solar cell to laser.

DOI:10.1049/ip-j.1986.0054

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A detailed optimisation procedure is described for high power, low threshold current density operation of asymmetric four-and five-layer large optical cavity lasers. The analysis of these multilayer waveguides is simplified by using a computer model based on an admittance transformation technique, commonly used in microwave circuit analysis. Effects of compositional and thickness variations on the waveguiding properties are described. The maximum obtainable output power scales with the width of the waveguide, although this results in an increase in threshold current density due to the decreased coupling between the optical distribution and the active layer. If the structure is designed to guide light in the absence of the active layer then the sensitivity of the optical properties to changes in active layer thickness is reduced, providing the active layer is kept thin. Examples of optimised structures are given to illustrate the effects various structural changes have on the optical properties of the device and on the threshold current density.

DOI:10.1049/ip-j.1986.0055

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A method for the design of a source, fibre and detector system, which is free from distortion due to stimulated Raman scattering, is proposed. The maximum transmission length and optimum loss value are predicted for a known input power level in dimensionless plots which clearly distinguish the operating region free of stimulated Raman scattering. Circumstances in which the losses at the pump and Stokes wavelengths are unequal are considered.

DOI:10.1049/ip-j.1986.0056

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Wave propagation through a slab dielectric waveguide with two periodic perturbations of the permittivity of very different amplitude but similar pitch is considered. The pitch of the weaker perturbation is chosen so that it lies in that part of the dispersion characteristic of the guide that is strongly distorted by the presence of the stronger perturbation. Coupled mode theory is used to analyse this situation, in which the spectral components of the index perturbation can no longer be taken to be independent of each other. Hence it is shown that the reflection bandwidth of the weak perturbation is narrowed by this particular configuration. The bandwidth decreases as the two pitches approach one another, but an effective limit on narrowing is imposed by the relatively strong side lobes of the reflectance of the strong pertyrbation.

DOI:10.1049/ip-j.1986.0057

出版商:IEE    

年代:1986

数据来源: IET