摘要:

A new Rayleigh quotient, which was introduced and briefly considered in a previous paper, is now examined in greater detail. When used in conjunction with polarised finite difference schemes established in earlier papers, it enables semivectorial E-field and H-field propagation modes of waveguide structures, which may contain any arbitrary distribution of horizontal and vertical dielectric discontinuities, to be determined without the need to solve matrix eigenvalue problems. The absence of a matrix enables the finite difference grid to incorporate substantially more points and smaller step lengths, thereby improving the accuracy of computed solutions. Results are presented for single rib waveguides and for rib waveguide directional couplers fabricated from III-V semiconductors.

DOI:10.1049/ip-j.1991.0032

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A novel integrated dielectric filter-photodiode is reported, together with the first results of reliability testing of the device. The filter-photodiode has been designed as a low-cost demultiplexing element for use in passive optical local networks. It combines an evaporated multilayer filter structure and a conventional planar InGaAs PIN photodiode in a single device. Results of initial reliability stress-tests indicate that good reliability can be expected from the device in service, even when operated in a non-hermetic package.

DOI:10.1049/ip-j.1991.0033

出版商:IEE    

年代:1991

数据来源: IET

摘要:

Theories of the spectral output of diode lasers assume that the devices are uniform along the length of the active region. Spatially-resolved degree of polarisation measurements are presented which show that devices are not uniform along the length and that significant scattering exists along the length of the active region. The spectral output of lasers is found to be correlated with the amount of scattering in the active region. Calculations to support and explain the observed correlation are presented. For the devices tested, it is found that gain guided devices tend to exhibit less scattering than index guided devices and tend to operate more multi-longitudinal mode. Based on these measurements it is suggested that differences in the spectral properties of index and gain guided lasers may be explained on the basis of the light scattering characteristics of the active region.

DOI:10.1049/ip-j.1991.0034

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The coupling between two parallel infinite gyroelectric cylinders is investigated analytically. The dyadic Green's function for a gyroelectric cylinder is used to formulate the integral equation that governs the coupled electromagnetic propagation. Cylindrical vector wavefunctions are used to expand the propagating waves inside and outside the gyroelectric cylinders. Appropriate manipulation of the resulting integral equation leads to a homogeneous linear infinite set of equations for the unknown electric field expansion coefficients. This set is truncated and the propagation constants of the propagating modes that the configuration may support are determined from the zeroes of its determinant. The corresponding equation is solved numerically. Numerical results are presented concerning the dependence of the propagation characteristics on various parameters of the configuration. Finally numerical results are presented and discussed.

DOI:10.1049/ip-j.1991.0035

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A treatment of the behaviour of TE nonlinear waves guiding in asymmetric dielectric hollow waveguides with a self-focusing Kerr-like nonlinear film is given. The mathematical results are derived by introducing the physical parameter which depends upon both the optical power density at the peak of the electric field profile and the dielectric constant difference between the film and the substrate, and relating the field amplitudes at the film boundaries to the wave number in the film. For three TE0waves, the dispersion curves, the electric field profiles, the cut-off frequency, the wave index and the guided power are illustrated and discussed. In addition, the effects of the waveguide asymmetry on the wave index for three TE0waves are discussed.

DOI:10.1049/ip-j.1991.0036

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A numerical modelling of SAM-APDs which takes into account the effects of the guard ring on the electric field profile is presented. Starting from the knowledge of the technological parameters and from a one-dimensional model, for which Poisson's and continuity equations have been treated, we calculate the gain, the dark current, and the cut-off frequency of the device, so that it is possible to deduce the limits of those parameters to avoid parasitic breakdowns at the centre of the diode, and to get structures with high gain-bandwidth products. A two-dimensional model based on numerical solution of Poisson's equation to study the electric field profile under the guard ring is developed. Optimal conditions for implantation are deduced to avoid breakdown at the edge of the junction curvature. The results given by this modelling are compared with the experimental results concerning SAM-APDs with guard ring, which have been fabricated by C.I.T. ALCATEL.

DOI:10.1049/ip-j.1991.0037

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A finite-element method using the Hermitian line elements is proposed for the analysis of planar diffused optical waveguides. In the Hermitian line elements, both the field and its derivative are considered at the nodal point. Therefore, the continuity of the field and its derivative between elements can be satisfied. To show the accuracy of the method, a planar diffused optical waveguide with exponential index profile is analysed, and the results obtained are compared with the results of the earlier finite-element method using the Lagrangian elements and the exact solutions. In the Hermitian finite-element method, the computation cost can be significantly reduced.

DOI:10.1049/ip-j.1991.0038

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A recently developed moment generating function (MGF) characterisation for a laser preamplified optical receiver is employed to effect rigorous performance assessment in terms of sensitivity and decision threshold setting. A modified Chernoff bound (MCB) is used as the basis for error probability estimation and a comparison with the simple Gaussian approximation (GA) is effected. The GA is shown to predict accurately receiver sensitivity but to indicate inappropriately low decision threshold levels when signal-dependent noise is significant.

DOI:10.1049/ip-j.1991.0039

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The device structures, operation principles, optoelectronic characteristics, performance comparisons, and possible applications for various a-Si:H/a-SiC:H phototransistors and avalanche photodiodes are reviewed. Although these devices are made of amorphous semiconductors, its majority-carrier transport properties can tactfully avoid gap-state and defect related minority-carrier transport problems, and obtain good performances. Also, each of these devices has the distinct advantage of meeting the requirements of different practical applications. The unique and distinct advantages of these a-Si:H/a-SiC:H devices are first, a variety of peak response wavelengths are achievable by changing the composition or the well-to-barrier widths of the superlattice, secondly, a large-area-detector image sensor can be made on a glass substrate; and thirdly, the low-temperature of the amorphous films (~250°C) possesses a very abrupt composition change and a doping profile, which are impossible in the single-crystalline semiconductors.

DOI:10.1049/ip-j.1991.0040

出版商:IEE    

年代:1991

数据来源: IET

摘要:

This article presents the optical pulse response analysis of a fibre ring resonator. It is shown that several interesting functions, namely optical pulse differentiation, integration or delay, trigger pulse generation, and equalisation of fibre dispersion can be realised by using the resonator. The theory is presented in an easy to understand manner, by first considering the steady-state response. The results of the transient pulse response are explained in relation to the steady state results. The results related to optical pulse shaping will be of interest to the future when coherent optical pulse and switching circuits will become available.

DOI:10.1049/ip-j.1991.0041

出版商:IEE    

年代:1991

数据来源: IET