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Optoelectronics, IEE Proceedings J

Issue 2 • Date Apr 1990

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Displaying Results 1 - 8 of 8
  • Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape

    Publication Year: 1990 , Page(s): 89 - 96
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. The paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. The authors present original results for a 50 Mbit/s, 1.3 μm wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM systems View full abstract»

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  • Noise characteristics of a new heterojunction avalanche photodiode

    Publication Year: 1990 , Page(s): 97 - 100
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    The new structure under consideration is similar to a double velocity avalanche transit time (DOVATT) diode. DOVATT is basically a heterojunction IMPATT diode which consists of one avalanche zone followed by two drift zones having different scattering limited velocities. Recent studies have shown that the structure can be used efficiently as a detector in optical communication systems. The new detector has been given the name photo-DOVATT. The paper examines the noise behaviour of the device. A quantitative study of the noise generated caused by randomness of multiplication process in the avalanche zone of an InP/InGaAsP photo-DOVATT has been carried out. It is observed that the device shows less noise voltage and higher signal to noise ratio (SNR) compared with other existing avalanche photodiodes View full abstract»

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  • Turning-point method of optimised multilayer design

    Publication Year: 1990 , Page(s): 101 - 107
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Arbitrary design specifications often result in conflicting requirements, which are physically mutually exclusive. By restricting the design objective to equiripple response in the passband, the author develops a method that accommodates the natural properties of the multilayer. This is accomplished by allowing the passband transmittance maxima and minima of a fixed-index multilayer to settle in their equilibrium positions appropriate to its physical nature. Transmittance adjustment takes place at the passband extremes, which are continually tracked during the refinement process, hence the name turning point method. Control of transmittance at these key points ensures wideband capability for both lowpass and highpass filters. The multilayers thus designed are optimum in the Chebychev sense View full abstract»

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  • Narrow band rib waveguide grating resonator filters

    Publication Year: 1990 , Page(s): 132 - 138
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Coupling coefficients for periodically corrugated GaAs/GaAlAs rib waveguides have been determined using a finite element technique and coupled-mode theory. Results are used to calculate the frequency response of resonator filters. The influence of resonator losses and output facet reflection on filter performance are discussed View full abstract»

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  • Use of reflected light for low data rate upstream signalling in a single mode passive optical network

    Publication Year: 1990 , Page(s): 108 - 114
    Cited by:  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    Assesses the feasibility of using reflected downstream light for upstream signalling in a primarily broadcast passive optical network, to eliminate the need for a light source at each terminal. It shows (for a typical CATV network) that using this technique, and by extracting only 1 dB from light power received at the customer's terminal, a mean upstream signalling rate of around 64 kbits/s from 32 terminals is possible. However, this requires full network synchronisation and modulation at the terminals at 2 Mbaud. In practice, the modulation of the reflected light may be limited to perhaps 1 kbaud if a cheap technology is to be employed. Under these circumstances, the maximum data rate is approximately 550 bits/s and is achieved using subcarrier FDMA. The use of subcarrier FDMA has the added advantage of providing completely asynchronous access from all terminals View full abstract»

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  • Effects of local oscillator excess noise, laser phase noise and time jitter on digital signalling schemes in coherent optical fibre communication systems

    Publication Year: 1990 , Page(s): 115 - 123
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    Investigates performance of heterodyne detection type coherent optical-fibre communication systems for binary and M-ary PSK, FSK and ASK digital signalling schemes, considering shot noise, local oscillator (LO) excess noise, laser phase noise and time jitter. Expressions for probability of error when LO excess noise, laser phase noise and time jitter are present as well as shot noise, are derived. Power penalties are also obtained in each case. Finally, the three signalling schemes are compared. The binary PSK is found to be the most efficient among the three signalling schemes. However, when laser phase noise is large, M-FSK and M-ASK signalling schemes give better performance than the M-PSK signalling scheme. The M-FSK scheme is found to require a larger bandwidth, and the M-ASK scheme is less immune to time jitter View full abstract»

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  • Considerations on geometry design of surface-emitting laser diodes

    Publication Year: 1990 , Page(s): 129 - 131
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    The paper presents comments on Baets' paper (see ibid., vol.135, p.233-41, 1988) which reports an analysis of surface-emitting (SE) diode laser operation. Baets' thermal model of the SE laser appears to overvalue the active area temperature increase of the laser to a considerable extent. The paper attempts to illumine some errors which may exist in Baets' model. The thermal model of a Burrus-type light-emitting diode (B-LED), published recently, is adapted for this case, i.e. for the thermal analysis of the SE laser. In the B-LED model, a current-spreading effect, a two-dimensional heat spreading, a radiative transfer of the spontaneous energy as well as a temperature dependence of a thermal conductivity are taken into account whereas a Joule heating is neglected View full abstract»

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  • Effect of optical radiation and surface recombination on the RF switching parameters of a GaAs MESFET

    Publication Year: 1990 , Page(s): 124 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    The study shows that the internal gate source capacitance increases with increasing radiation flux density under enhancement mode, and decreases under depletion mode. However, the surface recombination slightly reduces these effects. Further, the drain source resistance ( Rds) reduces with increasing radiation flux density at a particular trap centre density and increases with increasing surface trap density at a fixed flux density. It is also observed that the RC time constant decreases with increasing trap densities at a fixed flux density and absorption coefficient. The variation with doping density is also found to be of a decreasing nature for different flux densities and trap centre densities. At a fixed doping density, RC time constant is higher for higher flux density and lower trap density View full abstract»

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