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Optoelectronics, IEE Proceedings -

Issue 2 • Date Apr 1995

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Displaying Results 1 - 9 of 9
  • 2D optical fully bipolar neural network using colour encoding

    Publication Year: 1995 , Page(s): 121 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    A new architecture for implementing the bipolar interconnection weights and bipolar neuron states of an optical neural network is introduced. By using a proper light source and encoding the polarities of the interconnection weights and neuron states with colour films, the fully bipolar operations of a neural network can be performed optically View full abstract»

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  • Mode behaviour on bent planar dielectric waveguides

    Publication Year: 1995 , Page(s): 115 - 120
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A nonperturbative analysis of the field and propagation constant changes in a bent step index planar waveguide is presented, with the aim of investigating limitations on standard perturbation theory. Mode behaviour for two extreme regimes in which perturbation theory is no longer valid are demonstrated: single-mode guides with very small bend radius (~1 mm), in which the field in the cladding becomes oscillatory, and large multimode structures bent with a constant radius of curvature. Equations are derived for the dispersion relation whose solutions give the real propagation constant of the bent waveguide View full abstract»

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  • Thermal modelling of vertical-cavity surface-emitting lasers using the finite-element method

    Publication Year: 1995 , Page(s): 82 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    A self-consistent thermal model for a vertical-cavity surface-emitting laser (VCSEL) is presented using the powerful finite-element method. Temperature profiles for the etched-wall VCSELs are obtained iteratively, after considering their temperature-dependent material properties and the spatial distribution of all the significant heat sources View full abstract»

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  • Signal self-restoration characteristic and bit error rate performance of terrestrial cascaded erbium doped fibre amplifier systems

    Publication Year: 1995 , Page(s): 94 - 96
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    A normalised gain formula of perturbed erbium doped fibre amplifier (EDFA) is derived. For terrestrial systems where EDFAs work under low saturation, it is shown that optical power can regain 90% of its original value within three stages when the system suffers a 3 dB dip of EDFA output power. On the other hand, the corresponding system BER will be deteriorated by more than two orders of magnitude and the later the perturbation starts the more degradation in BER. Less saturated EDFAs would result in worse BER under the same perturbation View full abstract»

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  • VCSEL diffraction-loss theory

    Publication Year: 1995 , Page(s): 77 - 81
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    Mode matching in the Fourier spectral domain is used to obtain an expression for the reflectivity between the active cavity and the Bragg mirror of a mesa-geometry VCSEL. The variation of incident mode reflectivity with various parameters is discussed. Diffraction losses are evident, and the reflectivity can be significantly lower than the plane-wave value (the value commonly used) depending on the transverse dimensions of the active waveguide cavity View full abstract»

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  • Comparative analysis of the performance limits of Franz-Keldysh effect and quantum-confined Stark effect electroabsorption waveguide modulators

    Publication Year: 1995 , Page(s): 109 - 114
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    The author systematically analyses and compares the performance limits of quantum-confined Stark effect (QCSE) and Franz-Keldysh effect (FKE) electroabsorption waveguide modulators, in terms of insertion loss, contrast ratio, drive power and bandwidth (or bit-rate). The author first derives the universal material figures of merit for electroabsorption modulators which form the basis for comparison. In addition to the magnitude of electroabsorption Δα, the critical material parameters are Δα/α0 and Δα/F2 where α0 is the onstate residual absorption, and F is the applied electric field. The author proposes a waveguide design which will meet the insertion loss and contrast ratio requirements while minimising the available power/bandwidth (Pac/Δf) ratio. The author shows that, while satisfying the same insertion loss requirement, a QCSE modulator employing the optimum quantum well structure can have, in principle, an order of magnitude better performance in terms of Pac/Δf than one based on FKE. Correspondingly, the Δα/F2 is an order of magnitude larger in QCSE than in FKE, principally because of the much larger absorption change that is possible with QCSE View full abstract»

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  • Single mode power and modal behaviour in buried vertical-cavity surface-emitting lasers

    Publication Year: 1995 , Page(s): 87 - 93
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    Modal behaviour in buried vertical cavity surface-emitting lasers (VCSELs) is simulated using the two-dimensional beam-propagation-method (BPM) model. For broad-area VCSELs a tapered cavity strongly enhances the modal losses of the higher order modes and increases single mode output power. However, for small-area VCSELs it reduces output power. Furthermore, passive antiguide-region structure increases modal discrimination. An optimum index difference (Δ=0.084) is needed to achieve the maximum modal discrimination in the step-profile case. A new parameter, relative modal loss difference, is introduced to describe the mode competition, which can be used to estimate single-mode operation regime. The parameter can also be used in the external cavity case. Simulations show that a carefully designed 16 μm diameter antiguide-region lasers can operate in single mode in the whole bias region View full abstract»

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  • Asymmetric power coupling in grating-assisted couplers

    Publication Year: 1995 , Page(s): 103 - 108
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Asymmetric power coupling in grating-assisted coupler filter is revealed analytically for the first time by coupled-mode theory. An optimum grating period is then proposed and various coupling lengths for maximum power transfer and minimum crosstalk between two waveguides are derived analytically. Comparisons between coupled-mode theory and the vector beam propagation method have been made for possible scenarios of power exchange between the two waveguides. Excellent agreement between them indicates that the coupled-mode theory shown in the paper is able to not only reveal all the physics embedded in the complicated coupling processes, but also predict various possible filtering responses accurately View full abstract»

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  • Effects of lateral modes on the static and dynamic behaviour of buried heterostructure DFB lasers

    Publication Year: 1995 , Page(s): 97 - 102
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    The transient response of buried-heterostructure distributed-feedback laser is studied. It is found that the gain margin between the lateral modes is affected by the carrier-diffusion length in the active region. In addition, the transient response of the lateral modes is also influenced by the carrier-diffusion length View full abstract»

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