H. M. Gupta

Semiconductor optical amplifiers in WDM tree-net

In this paper, effectiveness of semiconductor optical amplifiers (SOAs) in tree-net in terms of increase in the number of users has been investigated. In the analysis, SOAs with (i) unsaturated gain, (ii) average gain saturation, and (iii) average gain saturation with gain fluctuations have been considered. Further, the results for the tree-net are compared with those for the star network. It is observed that tree-net supports more number of users than star for a given number of SOAs.

Receivers. Receiver Performance in Noise and ISI for Fiber Optic Communication System

Summary In this paper the performance of a digital optical receiver consisting of an avalanche photodiode has been evaluated in the presence of noise and the intersymbol interference (ISI). The ISI levels have been computed for a multimode step index fiber for various lengths and data rates and the results are presented in the graphical form. Improvement in the receiver performance with an equalizer has also been worked out.

Optical Amplifiers in Broadcast Optical Networks: A Survey

Optical data networks are needed to meet ever increasing bandwidth requirements. Broadcast optical networks can provide easy and reliable implementation of optical networks, but due to limited power budget, the number of users supported are limited. The optical amplifiers (OAs) can be used to Increase the number of users supported by the network. In this paper use of semiconductor optical amplifiers (SOAs) and doped fiber amplifier (DFAs) is being surveyed in several broadcast topologies, e.g. bus, star, tree etc.

Reed solomon code and semiconductor optical preamplifier in OOK communication system : A comparative study

In this paper, performance of OOK communication system with Reed-Solomon (R-S) (31,27,2) code and semiconductor optical amplifier (SOA) has been analyzed. In the analysis, effect of intersymbol interference (ISI) due to Gaussian filter in the receiver has been considered. It is observed that the use of SOA is much more advantageous than coding scheme. For a BER of 10 -9 , the coding gain is 1.7 dB, while the gain due to optical preamplifier is 21.2 dB.

Power penalty due to optical amplifier induced crosstalk in noncoherent OOK transmission system

In this paper, analysis of direct detection (DD) receiver with an optical preamplifier has been carried out for OOK signalling scheme. Effect of crosstalk due to adjacent channel has been considered along with the amplifier noise. It has been observed that there is a considerable improvement in the receiver sensitivity after the use of an optical preamplifier. Presence of crosstalk signal may reduce this sensitivity gain substantially.

Performance of Heterodyne Coherent Optical Fiber Communication Systems in Presence of Shot Noise, LO Excess Noise, Laser Phase Noise and Time Jitter

In this paper performance of heterodyne detection type coherent optical fiber communication systems for MPSK signalling scheme has been investigated. Expressions for probability of error in presence of shot noise have been modified to include the effect of local oscillator (LO) excess noise, laser phase noise and time jitter. Power penalties have also been obtained in each case. It has been, found that degradation of system performance due to laser phase noise increases significantly as value of M increases. However, degradation due to LO excess noise and time jitter is almost same for all values of M. It has been shown that higher power LO source are preferable from LO excess noise point of view. It is found that the effect of laser phase noise is significantly degrading as M increases in M-PSK systems. The power penalty due to time jitter does not vary significantly with M.

Multipoint Multimedia Communication

Multipoint multimedia communication is the underlying technology for a number of applications like video-conferencing and collaborative computing. In this paper, we have explored the networking requirements for multimedia applications and classified the latter accordingly. Some contemporary network technologies have been evaluated for their suitability towards multipoint multimedia applications. Two important technical aspects of such communication, namely synchronisation and multicasting, have been examined in greater detail. We present some case studies of multimedia network implementations and analyse their merits. Finally, the technology trends are discussed.

Laser Linewidth Requirements in Optical Binary Phase Shift Keying Communication Systems with Reed-Solomon Code

In this paper, effect of Reed-Solomon (R-S) code on the performance of optical binary phase shift keying (PSK) communication system has been analysed. Coding gain in terms of laser linewidth relaxation factor and reduction in the required optical power level has been determined. It has been observed that when R-S(31,27,2) code is used, coding gain in terms of laser linewidth relaxation factor for 1 GBPS system at a BER of 10 -9 (required optical power -70.0 dBm at a laser linewidth of 3.7 MHz) is about 2.51, i.e. laser linewidth can be relaxed from 3.7 MHz to 9.3 MHz. When the coding gain is computed in terms of reduction in required optical power level for the above system, it is 8.3 dB, i. e. when the laser linewidth is 3.7 MHz, coded system will require a power level of -78.3 dBm instead of -70.0 dBm.

Evaluation of Error Rate Floors in Digital Coherent Optical Fiber Communication Systems due to Laser Phase Noise

In this paper error rate floors due to laser phase noise in coherent optical fiber communication systems are evaluated for binary and M-ary PSK, FSK and ASK digital signalling schemes. These are used to obtain the upper bounds on source linewidth for different data rates at a given probability of error.

Demonstration of Intersymbol Interference, Effect of Noise and Time Jitter in Baseband Digital Communication System

In this paper, a simple demonstration set up is described to display effects of intersymbol interference, channel noise and time jitter. The circuits for the pseudorandom sequence generator with time jitter, threshold detector and matched filter are given. For the purpose of determining the transmission error rate, digital decimal counter alongwith an error counting and display circuit are also given. Experimental set up for observing the eye pattern when a PRBS output with time jitter is transmitted through a noisy channel is described.