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Optoelectronics, IEE Proceedings -

Issue 2 • Date Aug 1999

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Displaying Results 1 - 7 of 7
  • Feasibility of integrated optical isolator with semiconductor guiding layer fabricated by wafer direct bonding

    Page(s): 105 - 110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    An integrated optical isolator, employing a nonreciprocal phase shift, fabricated by wafer direct bonding technique is proposed. The optical isolator has an optical interferometer, which is composed of two tapered couplers, nonreciprocal phase shifters in two arms and a reciprocal phase shifter in one of the arms. The magneto-optic waveguide in the nonreciprocal phase shifter has a magnetic garnet-GaInAsP-InP structure, which is realised by the direct bonding technique. The theoretical and experimental results of the components for the isolator are demonstrated to investigate the feasibility of this device View full abstract»

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  • Hub architecture for infra-red wireless networks in office environments

    Page(s): 78 - 82
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    The paper describes a LOS system architecture that allows for a data rate of 155 Mbit/s on both down- and up-links. To achieve this, arrays of vertical cavity surface emitting lasers (VCSELs) are used that emit light of 850 nm and have an output power that is within eye-safety limits. Original theory is presented that permits calculation of the coverage area for a certain launch power and receiver sensitivity. Design equations are presented for the selection of the beam shaping/spreading lens placed in front of the laser arrays. Original results from an experimental testbed compare favorably with theoretical predictions. It is concluded that an 8×8 laser array will cover an area of 1 m by 1 m. The addition of a tracking system would permit multiuser operation with each individual user having access to the full bandwidth of the link View full abstract»

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  • Optical characterisation of quantum well infra-red detector structures

    Page(s): 89 - 92
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Optical characterisation of GaAs-AlGaAs quantum well infra-red photodetector (QWIP) structures by interband photoluminescence (PL) spectroscopy has been performed. The effect on the low temperature PL spectrum of both the doping concentration in the wells and the presence of thin lateral barriers is analysed. In addition to the main peak (e1-hh1), a second peak at lower energy is observed in doped structures and attributed to a donor-to-acceptor transition. The broadening of the e1-hh1 peak when the doping in the wells is increased is interpreted in terms of the bandfilling effect in the wells. An additional broadening appears when thin lateral barriers with higher content are introduced in the structure. Responsivities as high as 0.5 A/W without external coupling mechanisms of the incident light have been measured in samples showing the above-mentioned features in the PL spectra View full abstract»

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  • Estimation of frequency response for high-speed LiNbO3 optical modulators

    Page(s): 99 - 104
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A method of directly measuring the optical sideband in modulated output light by using an optical spectrum analyser is described for quantitatively estimating frequency responses of LiNbO3 optical modulators in a practical large-signal operation. The conventional methods of estimating microwave power from photo-detectors using an electrical network analyser or an electrical sampling oscilloscope are theoretically compared with the method of using an optical spectrum analyser. The frequency responses measured with the method that uses an optical spectrum analyser are shown to correspond consistently to the small-signal modulation for any value of modulation index in measurements and to be useful in estimating precisely the frequency response of ultra-high-speed optical modulators. The responses estimated with the conventional methods mentioned above depend on the modulation index at a larger-signal modulation of m0>~0.1. In particular, the responses when an electrical sampling oscilloscope is used vary remarkably with the value of m0. These analyses make possible accurate estimation of the LiNbO3 modulator's frequency response, and thus aid in its practical use in large-signal operation of pulse modulation View full abstract»

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  • Sub-picosecond gain dynamic in highly index-guided tapered-waveguide laser diode optical amplifiers

    Page(s): 83 - 88
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    The sub-picosecond gain dynamic in a highly index-guided tapered-waveguide laser diode amplifier is studied. The analysis is based on a set of rate equations for the carrier density N and carrier temperature T, where the effects of lateral distributions of both N and Tare considered. It is found that both N and T have significant effects on the gain dynamic of the tapered-waveguide laser diode amplifier. The gain saturation of the tapered-waveguide amplifier for both 20 ps and 200 fs pulses is also calculated View full abstract»

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  • Estimation of multiple-quantum well laser parameters for simulation of dispersion supported transmission systems at 20 Gbit/s

    Page(s): 93 - 98
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    In this paper, a set of multiple-quantum well (MQW) laser parameters is proposed for simulation of optical transmission systems at 20 Gbit/s. The parameters have been estimated by joint fitting of a small signal intensity modulation (IM) response model to five measured IM response curves of a strained layer MQW laser, using the Levenberg-Marquardt method. Good agreement between theoretical and experimental curves was obtained. Using these laser parameters, we have assessed the performance of dispersion supported transmission systems at 20 Gbit/s incorporating an erbium doped fibre amplifier (EDFA) or a semiconductor optical amplifier (SOA) as a booster amplifier. It is shown that the use of a SOA, with an unsaturated gain of 20 dB, improves the system performance for link lengths ranging from 8 to 20 km of standard single mode fibre (SMF) due to partial chirp compensation in the SOA, and degrades the system performance between 1.2 and 2.5 dB for link lengths ranging from 30 to 50 km. The increase of the unsaturated gain of the SOA from 20 to 25 dB is only advantageous for link lengths ranging from 8 to about 12.5 km where a small performance improvement, less than or equal to 0.8 dB, is observed. The influence on the system performance of an increase of the laser line width enhancement factor from 2 to 3 is also investigated View full abstract»

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  • Finite element modelling of electromagnetic waves in doubly and triply periodic structures

    Page(s): 111 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    A weighted residual finite element method (FEM) is employed to obtain the dispersion curves of two-dimensional (2D) doubly periodic and three-dimensional (3D) triply periodic structures (such as those employed in photonic band gap devices). The scalar and vector finite element formulations used in the computations are given. FEM results of 2D and 3D models are presented in a structured manner, which confirms the correct functioning of the finite element codes View full abstract»

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