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Optoelectronics, IEE Proceedings -

Issue 6 • Date Dec 1994

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Displaying Results 1 - 9 of 9
  • The SOUT optical intersatellite communication terminal

    Page(s): 345 - 355
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    Optical communications links between satellites promise to become an important element of future space infrastructure and are the subject of considerable development in Europe. Major advantages over conventional microwave links are low mass and power and smaller size leading to easier accommodation on the satellite. The Small Optical User Terminal (SOUT) is an optical communications package for interconnecting a low earth orbiting satellite to future optical data relay terminals and is the subject of an ESA development programme led by MMS (UK). The baseline terminal has a data rate of 2 Mbps over the return interorbit link and a mass of around 25 kg. The terminal configuration uses a unique combination of a periscopic coarse pointing assembly, refractive telescope, passive antivibration mount, combined acquisition and tracking sensor, and fibre coupled lasers and receivers. The paper discusses the design aspects for an asymmetric optical link based on the SOUT, covering link budgets, pointing, acquisition, and tracking and communications performance. Key SOUT subsystems are described and the structural and thermal configuration which allows these features to be combined in a compact unit is reported View full abstract»

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  • Jitter in the square synchroniser on direct detection optical communications. III. Numerical results concerning white circuit noise

    Page(s): 394 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    Theoretical assessment of the square synchroniser performance, developed in a previous paper, is used to present and discuss numerical results in the presence of white circuit noise. This fully analytical method permits the optimal design (i.e. minimising timing jitter) of square synchronisers. Taking into account all the relevant parameters, for direct detection optical communication systems, a thorough physical explanation of the presented results and their relevance for practical receiver design is provided. The work is increasingly important nowadays because multigigabit per second transmission rates are being used on direct detection optical systems. It is shown that, for low signal-to-noise ratios and under quite general conditions, the performance of the square synchroniser is better in a signal shot-noise-dominant situation (typical of long-distance communications with APD receivers), followed by the white-circuit-noise-dominant situation (typical of long-distance communications with PIN receivers), and is worst for the dark current-noise-dominant situation (typical of germanium APD receivers). The noise contribution to square synchroniser performance can be very high. The timing jitter properties respecting the circuit noise dominant situation usually hold also on the signal shot-noise dominant situation, except for a very narrow (compared with the bit period) optical pulse shape incident on the photodetector View full abstract»

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  • Silicon-on-insulator optical rib waveguides: loss, mode characteristics, bends and y-junctions

    Page(s): 391 - 393
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    Optical rib waveguides with widths from 2.73 to 7.73 microns have been formed in SIMOX-based silicon-on-insulator (SOI) structures consisting of a 4.32 micron thick surface-silicon layer and a 0.398 micron buried-oxide layer. The effect of waveguide width, bend radius, y-junction splitting and interface roughness on loss and mode characteristics have been studied at wavelengths of 1.15 and 1.523 microns. The experimental results support the hypothesis that certain rib dimensions can lead to single-mode waveguides even though planar SOI waveguides of similar multimicron dimension are multimode. The propagation losses of waveguides 3.72 microns wide were found to be nominally 0.0 dB/cm and 0.4 dB/cm for the TE and TM modes, respectively, when measured at 1.523 microns, where the measurement error was ±0.5 dB/cm. This means that the loss is experimentally indistinguishable from pure bulk silicon. These results are thought to be the lowest loss measurements for silicon integrated optical waveguides reported to date View full abstract»

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  • Optimum prechirping conditions of externally modulated lasers for transmission on standard fibre

    Page(s): 363 - 366
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The frequency response of standard fibre is computed when the optical source is a semiconductor laser modulated both directly and externally. Such a simple modulation scheme should provide 150 km transmission span at 10 Gbit/s without any addition to present ASK systems. The optimum conditions are expressed by a simple relation between the Henry parameters of the laser and the modulator. The frequency-modulation efficiency of the laser and the ratio of modulation depth View full abstract»

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  • Travelling wave electrode optimisation for high speed electro-optic modulators using the Fourier series method

    Page(s): 381 - 390
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    The performance of Z-cut Mach-Zehnder high speed LiNbO3 amplitude modulators with a CPW travelling wave electrode, has been analysed and optimally designed in detail by the Fourier series method. The effect of electrode and buffer layer thickness on the electric field distribution in the substrate, effective microwave refractive index and characteristic impedance of CPW electrode, are discussed. Calculation shows that increasing the thickness of the electrode and SiO2 buffer layer can improve the phase velocity mismatch between electric and optical waves, and the drive power required by the modulator with thin buffer layer and thick electrode is lower than that required by the modulator with thick buffer layer and thin electrode. In the optimisation procedure the graphic method without iteration is used with the help of a software called “GRAPH”. The optimum rate of electrode width with gap is near by 0.75 and is independent of the rate of electrode thickness with gap. The on/off voltage lower than 4.1 V is achieved by a modulator with electrode length 59 mm for 18 GHz bandwidth View full abstract»

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  • Spun linear birefringence fibres and their sensing mechanism in current sensors with temperature compensation

    Page(s): 373 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A single-mode spun linear birefringence fibre is investigated as a periodic structure. By using coupled-mode theory, the modal fields and the propagation coefficients of the two eigenmodes in this fibre are given theoretically for the first time. A spun highly linear birefringence (SHB) fibre is capable of acting as a sensing coil of relatively high sensitivity and temperature stability in current sensors. The mechanism of compensation and the sensitivities of current with SHB fibres and temperature compensation are studied extensively with the above eigenmode theory. The relations of sensitivity and temperature stability to parameters of SHB fibres and light sources are derived. The averaging effect caused by the broadband spectrum of the light source, which effectively eliminate the temperature instability, is investigated quantitatively with the partial-coherent-light theory View full abstract»

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  • Single Mueller matrix description of the propagation of degree of polarisation in a uniformly anisotropic single-mode optical fibre

    Page(s): 367 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    Changes in the degree of polarisation are described by a single Mueller matrix. Both the monochromatic and quasimonochromatic cases are discussed. The authors show how the propagating degree of polarisation depends on the temporal coherence, the coupling coefficient, the differential propagation constant and the differential loss, of which the last two are taken as frequency dependent. A form factor Ψ is introduced, and the saturation level of the degree of polarisation along the fibre is linked to the temporal coherence, the differential propagation constant and the differential loss View full abstract»

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  • Optoelectronic differential multiplexer logic based on phototransistors/LEDs and its use in optical systems

    Page(s): 401 - 408
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Differential and single-ended operation are compared for optoelectronic logic based on phototransistors and LEDs. This demonstrates the advantages of operating differentially to obtain tolerant elements which do not require tuning. Fan-out levels and interconnection strategies for this logic are discussed leading to the adoption of local interconnections with a fan-out of four to support regular 2D logic arrays of 4-to-1 multiplexers. It is shown that 4-to-1 multiplexers not only minimise the number of elements required to perform a function but also minimise the number of interstage connections and the number of stages required. The flexibility and power of the logic functionality and interconnection approach are demonstrated for both combinatorial and sequential logic where the use of shared outputs leads to significant logic compaction. This considerably increases the functionality and parallelism offered by a system View full abstract»

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  • Analysis of linearly polarised modes in elliptical-core fibre

    Page(s): 356 - 362
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The linearly polarised (LP) modes in elliptical-core fibre have been analysed theoretically. It was found that the electromagnetic fields of the LP modes in elliptical-core fibre can be expressed as a combination of Mathieu and modified Mathieu functions. The modal characteristic equations and propagation constants are derived. The cutoff frequencies of several lower order modes have been calculated and their propagation characteristics plotted. The effects of core ellipticity on the modal cutoff values and mode transmissions are addressed View full abstract»

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