摘要:

The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. This 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. We 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.

DOI:10.1049/ip-j.1990.0017

出版商:IEE    

年代:1990

数据来源: IET

摘要:

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 present 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.

DOI:10.1049/ip-j.1990.0018

出版商:IEE    

年代:1990

数据来源: IET

摘要:

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 paper 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.

DOI:10.1049/ip-j.1990.0019

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper 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.

DOI:10.1049/ip-j.1990.0020

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper investigates performance of heterodyne detection type coherent optical-fibre communication systems for binary andM-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 andM-ASK signalling schemes give better performance than theM-PSK signalling scheme. TheM-FSK scheme is found to require a larger bandwidth, and theM-ASK scheme is less immune to time jitter.

DOI:10.1049/ip-j.1990.0021

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The effect of optical radiation and surface recombination on the RF switching parameters of a GaAs MESFET has been analysed. 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.

DOI:10.1049/ip-j.1990.0022

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper presents comments on Baets' paper 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.

DOI:10.1049/ip-j.1990.0023

出版商:IEE    

年代:1990

数据来源: IET

摘要:

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.

DOI:10.1049/ip-j.1990.0024

出版商:IEE    

年代:1990

数据来源: IET