V. M. Nandakumaran

Publications (14)1.72 Total impact

• Source

  Available from: ias.ac.in

  Article: Bidirectional communication using delay coupled chaotic directly modulated semiconductor lasers

  Bindu M. Krishna, Manu P. John, V. M. Nandakumaran
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  ABSTRACT: Chaotic synchronization of two directly modulated semiconductor lasers with negative delayed optoelectronic feedback is investigated and this scheme is found to be useful for efficient bidirectional communication between the lasers. A symmetric bidirectional coupling is identified as a suitable method for isochronal synchronization of such lasers. The optimum values of coupling and feedback strength that can provide maximum quality of synchronization are identified. This method is successfully employed for encoding/decoding both analog and digital messages. The importance of a symmetric coupling is demonstrated by studying the variation of decoding efficiency with respect to asymmetric coupling. KeywordsIsochronal synchronization-bidirectional communication-directly modulated semiconductor lasers-delayed optoelectronic feedback
  Pramana 04/2012; 74(2):177-188. · 0.57 Impact Factor
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  Available from: ias.ac.in

  Article: Effect of a fluctuating parameter mismatch and the associated time-scales on coupled Rossler oscillators

  Manu P. John, P. U. Jijo, V. M. Nandakumaran
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  ABSTRACT: We study the effect of parameter fluctuations and the resultant multiplicative noise on the synchronization of coupled chaotic systems. We introduce a new quantity, the fluctuation rate ϕ as the number of perturbations occurring to the parameter in unit time. It is shown that ϕ is the most significant quantity that determines the quality of synchronization. It is found that parameter fluctuations with high fluctuation rates do not destroy synchronization, irrespective of the statistical features of the fluctuations. We also present a quasi-analytic explanation to the relation between ϕ and the error in synchrony.
  Pramana 04/2012; 72(3):495-503. · 0.57 Impact Factor
• Source

  Available from: ias.ac.in

  Article: Performance characteristics of positive and negative delayed feedback on chaotic dynamics of directly modulated InGaAsP semiconductor lasers

  Bindu M. Krishna, Manu. P. John, V. M. Nandakumaran
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  ABSTRACT: The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically. The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range. Comment: 18 pages, 16 figures. To appear In Pramana - journal of physics
  08/2008;
• Source

  Available from: ArXiv

  Article: Chaos in an intermittently driven damped oscillator

  Manu. P. John, V. M. Nandakumaran
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  ABSTRACT: We observe chaotic dynamics in a damped linear oscillator, which is driven only at certain regions of phase space. Both deterministic and random drives are studied. The dynamics is characterized using standard techniques of nonlinear dynamics. Interchanging roles of determinism and stochasticity is also considered.
  01/2008;
• Source

  Available from: ArXiv

  Article: Effect of a fluctuating parameter mismatch in coupled R\"{o}ssler systems

  Manu. P. John, Jijo P. Ulahannan, V. M. Nandakumaran
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  ABSTRACT: This paper is concerned with the effect of parameter fluctuations with a characteristic waiting time in coupled R\"{o}ssler oscillators. We show that the averaged error in synchronization that is introduced due to a fluctuating parameter is proportional to the waiting time and the amplitude of the fluctuations. It is also shown that coupling strength beyond a threshold value does not have any significant effect on improving the quality of synchronization when the fluctuations posses considerable waiting time.
  08/2007;
• Source

  Available from: arxiv.org

  Article: Parameter fluctuations in coupled chaotic systems

  M. P John, P. U Jijo, V. M Nandakumaran
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  ABSTRACT: We study the effect of parameter fluctuations on synchronization of a coupled chaotic system. The fluctuations to the parameter can be random or it can be a periodic modulation. For random fluctuations we introduce a new quantity, the \emph{rate of fluctuations}, apart from the statistical features of the fluctuations. Fluctuation rate in our study refers to the number of random modifications to parameters occurring in unit time. With a periodic modulation, the fluctuation rates can be the frequency of the modulating term. It is found that with high fluctuation rates the synchronization is stable irrespective of the statistical or mathematical features of fluctuation. It was also found that the low fluctuation rates can destroy synchronization even with a small amplitude. We analytically explain the observed phenomenon using the dynamical equations and numerically verified with a coupled system of Rossler attractor as an example. We also numerically quantify the relation between synchronization error and fluctuation rates.
  05/2005;
• Article: Two dimensional large amplitude quasi solitons in thin helium films

  J. Sreekumar, V.M. Nandakumaran
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  ABSTRACT: Large amplitude local density fluctuations in a thin superfluid {sup 4}He film is considered. It is shown that these large amplitude fluctuations travel and behave like quasi-solitons under collision, even when the full nonlinearity arising from the Van der Waals potential is taken into account.
  Modern Physics Letters B; (USA). 12/1989; 4:1.
• Article: Solitons and their resonances on two-dimensional superfluid films

  J Sreekumar, V M Nandakumaran
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  ABSTRACT: The dynamics of saturated two-dimensional superfluid4He films is shown to be governed by the Kadomtsev-Petviashvili equation with negative dispersion. It is established that the phenomena of soliton resonance could be observed in such films. Under the lowest order nonlinearity, such resonance would happen only if two dimensional effects are taken into account. The amplitude and velocity of the resonant soliton are obtained.
  Pramana 04/1989; 33(6):697-704. · 0.57 Impact Factor
• Article: Suppression of chaos in a directly modulated semiconductor laser with delayed optoelectronic feedback

  S. Rajesh, V.M. Nandakumaran
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  ABSTRACT: The effect of delayed optoelectronic feedback on a directly modulated InGaAsP laser diode is numerically studied. It is found that a complete elimination of the previously observed period doubling, chaos and formation of pulses with double peak structure is possible by the feedback with small delays. Bifurcation diagrams and time series plots are used to characterize the chaotic and periodic states of the laser.
  Physics Letters A.
• Source

  Available from: inflibnet.ac.in

  Article: Dynamics of Nonlinear Waves on Superfluid Helium Films

  J Sreekumar, V M Nandakumaran
• Article: Control of bistability in a directly modulated semiconductor laser using delayed optoelectronic feedback

  S. Rajesh, V.M. Nandakumaran
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  ABSTRACT: We show numerically that direct delayed optoelectronic feedback can suppress hysteresis and bistability in a directly modulated semiconductor laser. The simulation of a laser with feedback is performed for a considerable range of feedback strengths and delays and the corresponding values for the areas of the hysteresis loops are calculated. It is shown that the hysteresis loop completely vanishes for certain combinations of these parameters. The regimes for the disappearance of bistability are classified globally. Different dynamical states of the laser are characterized using bifurcation diagrams and time series plots.
  Physica D: Nonlinear Phenomena.
• Article: Multi-user bidirectional communication using isochronal synchronisation of array of chaotic directly modulated semiconductor lasers

  Bindu M. Krishna, Manu P. John, V.M. Nandakumaran
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  ABSTRACT: Isochronal synchronisation between the elements of an array of three mutually coupled directly modulated semiconductor lasers is utilized for the purpose of simultaneous bidirectional secure communication. Chaotic synchronisation is achieved by adding the coupling signal to the self feedback signal provided to each element of the array. A symmetric coupling is effective in inducing synchronisation between the elements of the array. This coupling scheme provides a direct link between every pair of elements thus making the method suitable for simultaneous bidirectional communication between them. Both analog and digital messages are successfully encrypted and decrypted simultaneously by each element of the array.
  Physics Letters A.
• Article: Nonlinear Dynamics of Semiconductor LasersControl and Synchronization of Chaos:

  S Rajesh, V M Nandakumaran
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  ABSTRACT: Nonlinear dynamics of laser systems has become an interesting area of research in recent times. Lasers are good examples of nonlinear dissipative systems showing many kinds of nonlinear phenomena such as chaos, multistability and quasiperiodicity. The study of these phenomena in lasers has fundamental scientific importance since the investigations on these effects reveal many interesting features of nonlinear effects in practical systems. Further, the understanding of the instabilities in lasers is helpful in detecting and controlling such effects. Chaos is one of the most interesting phenomena shown by nonlinear deterministic systems. It is found that, like many nonlinear dissipative systems, lasers also show chaos for certain ranges of parameters. Many investigations on laser chaos have been done in the last two decades. The earlier studies in this field were concentrated on the dynamical aspects of laser chaos. However, recent developments in this area mainly belong to the control and synchronization of chaos. A number of attempts have been reported in controlling or suppressing chaos in lasers since lasers are the practical systems aimed to operated in stable or periodic mode. On the other hand, laser chaos has been found to be applicable in high speed secure communication based on synchronization of chaos. Thus, chaos in laser systems has technological importance also. Semiconductor lasers are most applicable in the fields of optical communications among various kinds of laser due to many reasons such as their compactness, reliability modest cost and the opportunity of direct current modulation. They show chaos and other instabilities under various physical conditions such as direct modulation and optical or optoelectronic feedback. It is desirable for semiconductor lasers to have stable and regular operation. Thus, the understanding of chaos and other instabilities in semiconductor lasers and their xi control is highly important in photonics. We address the problem of controlling chaos produced by direct modulation of laser diodes. We consider the delay feedback control methods for this purpose and study their performance using numerical simulation. Besides the control of chaos, control of other nonlinear effects such as quasiperiodicity and bistability using delay feedback methods are also investigated. A number of secure communication schemes based on synchronization of chaos semiconductor lasers have been successfully demonstrated theoretically and experimentally. The current investigations in these field include the study of practical issues on the implementations of such encryption schemes. We theoretically study the issues such as channel delay, phase mismatch and frequency detuning on the synchronization of chaos in directly modulated laser diodes. It would be helpful for designing and implementing chaotic encryption schemes using synchronization of chaos in modulated semiconductor laser
• Article: Soliton resonances in helium films

  J. Sreekumar, V.M. Nandakumaran
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  ABSTRACT: The phenomenon of two-soliton resonances of the Kadomtsev-Petviashvilli equation for the superfluid surface density fluctuation in He films is studied. The velocity of the resonant soliton is obtained.
  Physics Letters A. 112:168-170.