Dr. Pramod KUMAR, M.Phil., Ph.D. (Laser Tech.) | University of Exeter (original) (raw)

Videos by Dr. Pramod KUMAR, M.Phil., Ph.D. (Laser Tech.)

The equipment, which uses a CMOS detector, will enable mass-scale screening with results made ava... more The equipment, which uses a CMOS detector, will enable mass-scale screening with results made available in seconds,” said Dr Pramod Kumar, who leads the team of researchers at the lab which has been studying the change in cell structure of the virus-infected blood. In fact, our laser-based DPI [Diffractive Phase Interferometry] technique, based on optical-phase modulation, is able to give a signature of infection within a few seconds. What’s more, it is user-friendly, non-invasive and low-cost. We believe it will be a game-changer in tackling the spread of the coronavirus.

4 views

The equipment, which uses a CMOS detector, will enable mass-scale screening with results made ava... more The equipment, which uses a CMOS detector, will enable mass-scale screening with results made available in seconds,” said Dr Pramod Kumar, who leads the team of researchers at the lab which has been studying the change in cell structure of the virus-infected blood.
“In fact, our laser-based DPI [Diffractive Phase Interferometry] technique, based on optical-phase modulation, is able to give a signature of infection within a few seconds. What’s more, it is user-friendly, non-invasive and low-cost. We believe it will be a game-changer in tackling the spread of the coronavirus.”

11 views

QuantLase Imaging Lab, the medical research arm of International Holdings Company (IHC) listed on... more QuantLase Imaging Lab, the medical research arm of International Holdings Company (IHC) listed on the Abu Dhabi Stock Exchange, announced that it has developed novel devices that enable mass exams to be performed much faster, with test results available in seconds and testing at a larger scale enable. This breakthrough will enable “mass-scale screening” and thus change the entire dimension of traceability.

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Papers by Dr. Pramod KUMAR, M.Phil., Ph.D. (Laser Tech.)

Journal of Physics B: Atomic, Molecular and Optical Physics, 2008

We analyse the locking phenomena arising when an external-cavity diode laser is subjected to opti... more We analyse the locking phenomena arising when an external-cavity diode laser is subjected to optical injection from another uncontrolled diode laser. The system stability is investigated as a function of coupled cavity time delay and the optical injection strength. Different ...

Electroactive Polymer Actuators and Devices (EAPAD) 2014, 2014

ABSTRACT We experimentally and numerically probe the natural quasi-ordered complex structures in ... more ABSTRACT We experimentally and numerically probe the natural quasi-ordered complex structures in the transparent insect wings by a simple, non-invasive, real time optical diffraction technique using monochromatic cw lasers and broadband femtosecond laser pulses. A complex diffraction pattern in transmission unveils the signature of long range spatial correlation in structural arrangement (symmetry) at various length scales on the whole wing surface for a variety of insect wings. A quantitative analysis analysis of the Fast Fourier transform (FFT) angular spectrum reveals a direct link between the structural organization and optical transmitted diffraction patterns. Our findings directly demonstrate how the diffraction pattern through the transparent insect wings is spatially and functionally correlated with its structural origination at various length scales. The methodology of the studies developed in this paper is applicable to a wide class of disordered photonic structures.

Laser Physics Letters, 2015

Conference on Lasers and Electro-Optics (CLEO), San Jose, California, USA, 2016

We report effects of varying feedback ratios and phases in dual-loop external optical feedback o... more We report effects of varying feedback ratios and phases in dual-loop external optical
feedback on phase-noise characteristics of passively mode-locked two-section quantum-dash
lasers. Optimal feedback yields ~100x reductions in RF-linewidth.

Chaotic Modeling and Simulation International Conference (CHAOS), London, UK, 2016

In this work, we present experimental studies of complex nonlinear dynamics in mode- locked quan... more In this work, we present experimental studies of complex nonlinear dynamics in mode-
locked quantum-dash lasers subject to frequency dependent optical feedback with fixed
filtering. Filtered or dispersive optical feedback offers advantages over conventional
optical feedback as its provides specific controllable spectral content of feedback to
manipulate the laser dynamics, specifically by varying the filter bandwidth and detuning
from the free running mode-locked frequency, without introducing attenuating optics in
the feedback loop. In addition, we discuss how the various dynamical regimes of the
mode-locked laser with filtered optical feedback depend on the filter bandwidth and
frequency and also how the presence of particular dynamical states can induce a
significant change in the timing jitter of a mode-locked pulse train. We suggest that the
dynamics are manipulated and controlled by changes in phase-amplitude coupling, and
thus strong carrier dependence of the index on carrier density and varying with dispersive
optical feedback. Physically, when the free running mode-locking frequency is on the
blue side of the filter center frequency then the feedback induces a red-shift in frequency
with reduced phase-amplitude coupling factor α. Our technique provides a simple and
low cost way to effectively control the Rf dynamics of the mode-locked laser diode and
here its uses as an optical clock, lidar or frequency comb.

Optics Express, 2018

We report experimental studies of the influence of symmetric dual-loop optical feedback on the RF... more We report experimental studies of the influence of symmetric dual-loop optical feedback on the RF linewidth and timing jitter of self-mode-locked two-section quantum dash lasers emitting at 1550 nm. Various feedback schemes were investigated and optimum levels determined for narrowest RF linewidth and low timing jitter, for single-loop and symmetric dual-loop feedback. Two symmetric dual-loop configurations, with balanced and unbalanced feedback ratios, were studied. We demonstrate that unbalanced symmetric dual loop feedback, with the inner cavity resonant and fine delay tuning of the outer loop, gives the narrowest RF linewidth and reduced timing jitter over a wide range of delay, unlike single and balanced symmetric dual-loop configurations. This configuration with feedback lengths of 80 and 140 m narrows the RF linewidth by ∼ 4-67x and ∼ 10-100x, respectively, across the widest delay range, compared to free-running. For symmetric dual-loop feedback, the influence of different power split ratios through the feedback loops was determined. Our results show that symmetric dual-loop feedback is markedly more effective than single-loop feedback in reducing RF linewidth and timing jitter, and is much less sensitive to delay phase, making this technique ideal for applications where robustness and alignment tolerance are essential. "Quantum dash mode-locked lasers for data centre applications ," IEEE J. Sel. Top. Quantum Electron. 21(6), 53-60 (2015). 2. J. P-Cetina, S. Latkowski, R. M-.Basilio, and P. Landais, "Wavelength tunability of all-optical clock-recovery based on quantum-dash mode-locked laser diode under injection of a 40-Gb/s NRZ data stream," IEEE J. Sel. Top. Quantum Electron.

M utually delay-coupled semiconductor lasers system show a plethora of dynamical complexity in th... more M
utually delay-coupled semiconductor lasers system show a plethora of dynamical complexity in the emitted radiation due to phase-amplitude coupling factor alpha, α that make them ideal candidate for fundamental studies of coupled oscillators
as well as for practical applications ranging from optical communications to computing. On the one hand these dynamical instabilities are undesired features and disturb the many applications where one needs the constant stable high power but
on the other hand they may allow for new methods for secure communications using chaos synchronization. The variety of optical complexity in these systems which we have investigated theoretically as well as experimentally is well behaving, well
understandable, well classifiable in terms of complex nonlinear dynamics. So the systematic study and control of these nonlinea dynamics provides fundamental insight into the underlying physics of the system, on the basis of which one can redesign the device in order to stabilize the working point against environmental fluctuations or improve the processing, or simply exploit the dynamical performance of a system to one’s advantages.

We numerically demonstrate the effect of optical injection induced modulation of the phase-amplit... more We numerically demonstrate the effect of optical injection induced modulation of the phase-amplitude coupling (factor) on power spectra and optical characteristics in mutually coupled lasers system with finite delay. We observed the signature of tunable phase locked laser emission (coherent In-phase and Anti-phase) by directly controlling the nonlinearity via manipulating phase-amplitude coupling. In addition, we predict the occurrence of frequency discretization and multistability near the phase transitions regimes, which could be useful in guiding the design of both experimental setup and compact photonic integrated practical devices for the generation of higher power laser system with the aid of optical phase control.

IEEE , 2017

We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-se... more We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-section quantum dash lasers emitting at ~1.55 µm and operating at ~21 GHz repetition rate, subjected to single and dual loop optical feedback into the gain section, over a wide range of feedback delay. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual-loop configurations. We demonstrate that dual-loop feedback with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, 10 – 50× better than single-loop feedback. In addition, for dual-loop configurations, under fully resonant conditions, phase noise is reduced to 295 fs [10 kHz – 100 MHz], the RF linewidth narrows to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual-loop optical feedback with separate fine tuning of both external cavities is far superior to single-loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

We demonstrate a symmetric dual loop feedback scheme, insensitive to delay phase tuning, for a se... more We demonstrate a symmetric dual loop feedback scheme, insensitive to delay phase tuning, for a self-mode-locked quantum dash laser emitting at ~ 1.55 µm and operating at ~ 21 GHz repetition rate. These lasers are subjected to single and dual loop optical feedback into the gain section. Various feedback conditions are studied and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and symmetric dual loop configurations. We demonstrate that symmetric dual loop with the inner cavity fully resonant and the outer one slightly offset, produces narrowed RF spectra across the widest delay range. In general, symmetric dual loop feedback is far more effective than single loop feedback in reducing RF linewidth and timing jitter, across a much wider range of delay phase. Resonant conditions for dual loop feedback are nearly independent of delay, making it ideal for practical applications where robustness and tolerance to misalignment are essential.

arXiv, 2017

We investigate the influence of symmetric dual-loop feedback (loops with equal length) as a funct... more We investigate the influence of symmetric dual-loop feedback (loops with equal length) as a function of full delay tuning on the RF linewidth and timing stability of ~ 21 GHz self-mode-locked quantum dash laser. Various feedback scenarios are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both feedback schemes. Two symmetric dual-loop configurations, subject to balanced (equal feedback strength through either feedback cavity) and unbalanced feedback ratio (~ 4x more power through loop-I relative to other) are presented here. We demonstrated that unbalanced symmetric dual-loop, with the inner cavity fully resonant (at higher feedback intensity) and fine delay tuning of the outer loop (at lower feedback intensity), gives narrow RF linewidth and reduced timing jitter over a wide range of delay detuning, unlike single and balanced symmetric dual-loop configurations. This study reveals that unbalanced symmetric dual-loop with feedback delay lengths 80 and 140 m narrows the RF linewidth by ~ 4-67x (~ 2-9x timing jitter reduction) and ~ 10-100x (~ 2.5-10x timing jitter reduction), respectively, across the widest delay range, compared to free-running condition. The influence of symmetric dual-loop with balanced and unbalanced feedback ratio on the stability of the laser device is further discussed. These results suggests that symmetric dual-loop feedback with controlled feedback strength over each loop and without additional delay time in external feedback loops is significantly more effective than single loop feedback in reducing RF linewidth and timing jitter, across full range of delay phase tuning. Wider resonant feedback regime as a function of full delay tuning achieved with symmetric dual-loop configuration makes this technique ideal for practical applications where robustness and tolerance to misalignment are essential.

Opt. Express 25, 15796-15805 (2017)

We experimentally investigate the RF linewidth and timing jitter over a wide range of delay tunin... more We experimentally investigate the RF linewidth and timing jitter over a wide range of delay tuning in a self-mode-locked two-section quantum dash lasers emitting at ~ 1.55µm and operating at ~ 21 GHz repetition rate subject to single and dual optical feedback into gain section. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual loop configurations. We demonstrate that dual loop feedback, with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, unlike single loop feedback. In addition, for dual loop configurations, under fully resonant conditions, integrated timing jitter is reduced from 3.9 ps to 295 fs [10 kHz-100 MHz], the RF linewidth narrows from 100 kHz to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual loop optical feedback with separate fine tuning of both external cavities is far superior to single loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

CLEO: Science and innovation 2017, May 19, 2017

We demonstrate a novel dual-loop scheme to suppress external cavity side-bands and modal overlaps... more We demonstrate a novel dual-loop scheme to suppress external cavity side-bands and
modal overlaps induced in spectrum of self-mode-locked laser resulting from conventional single loop feedback and dual loop feedback configurations.

Proc. SPIE 10086, High-Power Diode Laser Technology XV, 100860Q (22 February 2017)

We numerically investigate the effect of phase-amplitude coupling modulation on power spectra in ... more We numerically investigate the effect of phase-amplitude coupling modulation on power spectra in semiconductor lasers subject to optical injection in a face to face configuration, when a non-negligible injection delay time is taken into account. We find that as phase-amplitude coupling factor α varies, the system goes through a sequence of phase transactions between In-phase locking states to anti-phase locking states via phase-flip bifurcation. Moreover, we observed the signature of frequency discretization (Frequency Island) and uncovered the physical mechanism for the existence of multi-stability near the phase transitions regimes. Within the windows between successive anti-phases to in-phase locking regions, optical injection induced modulation in alpha, unveiling a remarkable universal feature in the various dynamics of coupled lasers system which could be useful in controlling the chirp or pulse repetition rate of a photonic integrated compact device with the aid of phase control.

We probed the natural quasi-ordered complex photonics structures on the transparent insect wings ... more We probed the natural quasi-ordered complex photonics structures on the transparent insect wings of rainfly (Termite) by a simple, non-invasive, real time transmission optical diffraction technique using monochromatic CW lasers and broadband femtosecond laser pulses. Our observations directly demonstrate the coherent manipulation and control of light in these photonic systems and detail understanding of our observation could provide a platform for the development of novel photonic devices for biomimetic technological applications.

We have classified optically various structural symmetries including, circular, triangular, hexag... more We have classified optically various structural symmetries including, circular, triangular, hexagonal, random, and quasiperiodic in photonic structure organization on variety of insect wing surfaces via optical diffraction properties using monochromatic green laser and broadband femtosecond laser pulses. In conclusion, a detailed understanding of our observation about the classification of probed structural symmetries could provide a platform for the development of novel photonic devices for biomimetic technological applications [

4 views

The equipment, which uses a CMOS detector, will enable mass-scale screening with results made ava... more The equipment, which uses a CMOS detector, will enable mass-scale screening with results made available in seconds,” said Dr Pramod Kumar, who leads the team of researchers at the lab which has been studying the change in cell structure of the virus-infected blood.
“In fact, our laser-based DPI [Diffractive Phase Interferometry] technique, based on optical-phase modulation, is able to give a signature of infection within a few seconds. What’s more, it is user-friendly, non-invasive and low-cost. We believe it will be a game-changer in tackling the spread of the coronavirus.”

11 views

17 views

Journal of Physics B: Atomic, Molecular and Optical Physics, 2008

Electroactive Polymer Actuators and Devices (EAPAD) 2014, 2014

Laser Physics Letters, 2015

Conference on Lasers and Electro-Optics (CLEO), San Jose, California, USA, 2016

Chaotic Modeling and Simulation International Conference (CHAOS), London, UK, 2016

Optics Express, 2018

IEEE , 2017

arXiv, 2017

Opt. Express 25, 15796-15805 (2017)

CLEO: Science and innovation 2017, May 19, 2017

Proc. SPIE 10086, High-Power Diode Laser Technology XV, 100860Q (22 February 2017)

Sub-kHz RF-linewidth was demonstrated in two-section quantum-dash mode-locked lasers emitting nea... more Sub-kHz RF-linewidth was demonstrated in two-section quantum-dash mode-locked lasers emitting near 1550 nm and 20 GHz repetition-rate using symmetric dual-loop and fiber delay. Compared to free-running lasing, RF-linewidth and timing-jitter reduced by ~100x and ~10x.

CLEO: Science and Innovations 2016 San Jose, California United States 5–10 June 2016, Jun 3, 2016

We report effects of varying feedback ratios and phases in dual-loop external optical feedback on... more We report effects of varying feedback ratios and phases in dual-loop external optical feedback on pulse characteristics of passively mode-locked two-section quantum-dash lasers. Optimal feedback yields ~100x reductions in RF-linewidth.

We present an experimental investigation of the influence of biasing conditions on the mode-locki... more We present an experimental investigation of the influence of biasing conditions on the
mode-locking of a dual-section quantum dash laser in the presence of Gain–to-Absorber optical
feedback. Our investigations reveal that variations in the forward bias gain current and reverse bias absorbing voltage have a direct impact on the pulse duration, variability in RF linewidth and repetition frequency tunability. Our observation of optimal biasing conditions opens the way to applications requiring high stable, low noise pulses and unavoidable reflections from optical components in photonic integrated circuit.

Journal of Electrical Engineering and Electronic Technology, 2019

Many practical problems in all science and technological disciples have been classified as comput... more Many practical problems in all science and technological disciples have been classified as computationally NP hard like combinatorial optimization, prime factorization of large integer, finding the ground state of the Ising Hamiltonian. More specifically, some cryptographic algorithms such as RSA (Rivest–Shamir–Adleman) critically depends on the fact that the terrible difficulty for finding the prime factorization of large integer. A polynomial-time algorithm was invented by Shor for quantum computers. Is there any optical system able to compute such a factoring algorithm? Optical systems are perhaps the most robust and fastest accessible system capable of dealing Shor’s function. In this work, we have developed an optical platform of proof of concept experiment for period finding. We present an experimental and numerical observation, that demonstrate the prime factorization based on Shor’s algorithm using laser light. Scalability is one of the major strength inherent in this DMD (digital micromirror device) based technique. Although, this classical approach cannot compete with the quantum algorithm in terms of efficiency, quantum entanglement can potentially be used aiming at speeding up prime factorization for classical computers.

Optical Coherence is one of the most curcial characteristic of any laser source for various range... more Optical Coherence is one of the most curcial characteristic of any laser source for various range of applications in modern medical imaging technologies. Nevertheless in the context of biological or living systems imaging, high spatial coherence is a drawback, which is directly related to speckle pattern. In order to get rid of speckle in deep imaging, we need a desirable light probe with tunable wavelength, longitudinal and transverse coherence properties. In this context, natural complex photonic architectures at various lenght scale (nm-μm) with various geometries have a roused much interest in the scientific community for their promising impact on the manipulation and control of light for various Biophotonic applications [1, 2]. Seeing inspiration from nature, we have naturally found deeply grooved blazed micro-grating arrays on various transparent insect wing surfaces [3]. While the direct use of natural biophotonic structures for optical applications is limited since they are composed of bio-polymers with rather poor mechanical and photo stability, but the investigation of these structures allows both a better understanding of the host species evolutionary development and provides intriguing templates for biomimetic applications (reverse engineering). In this work, we proposed an efficient, cost-effective technique for tunable spatial coherence of VECSEL-based short pulse lasers on the spatially resolved measurement of a speckle field produced by the coherent interaction of the laser pulses with natural photonic structures. We found that the spatial coherence of our laser pulses varies significantly with the structural disorder. This work demonstrates the feasibility of utilizing OP-VECSEL with natural random medium, spatially tunable coherence light sources for applications in deep imaging technology [4, 5].
References:
[1] P. Kumar et al., "Optical Probing of Long Range Spatial Correlation and Symmetry of complex Bio photonic Architecture on Transparent Insect Wings," Laser Phys. Lett. 12, 025901 (2015).
[2] P. Kumar et al., Appl. Phys. Lett. 104, 063702 (2014).
[3] P. Kumar, WW-EAP Newsletter, Vol. 18, No. 1, June 2016 (The 35th issue).
[4] B. Redding, P. Ahmadi, V. Mokan, M. Seifert, Michael A. Choma, and H. Cao, "Low-spatial-coherence high-radiance broadband fiber source for speckle free imaging," Opt. Lett. 40, 4607-4610 (2015)
[5] P. Kumar, Laser Focus World Biophotonics: Optical probe characterizes biophotonic insect-wing structures (2015)

Royal Society Interface Focus issue, 2018

Natural photonic structures are fascinating templates for biomimetic designs for novel optical sy... more Natural photonic structures are fascinating templates for biomimetic designs for novel optical systems, components or devices to control and manipulate light such as blazed grating [1, 2]. Technically, it is very difficult to develop a transmission blazed micro-grating due to complicated fabrication process and other technical constraints on miniaturization. Seeing inspiration from nature, we have naturally found deeply grooved blazed micro-grating arrays on transparent insect wing (Rain-fly) surfaces. In this paper we demonstrate optical functionality of these blazed micro-grating probed using ultrashort laser pulses as well as monochromatic CW illumination. We experimentally and numerically study blazed micro-grating structures on surface of transparent insect wings, and demonstrate their coherent optical functionalities. We observe blazed diffraction properties which strongly depend on individual micro-gratings geometry. In order to support our experimental observation, we have considered Huaijun Wang’s theoretical model for the diffraction of blazed transmission grating with moderate period [3]. Our observation may open up new opportunities in biomimetic device research for the design optical components for photonic integrated system.

It is well known that the dynamics of a neuronal network often involves time delay due to the fin... more It is well known that the dynamics of a neuronal network often involves time delay due to the finite signal propagation time in biological networks and diversity in terms of morphology and function, which makes neuronal network attracts more and more theoretical concerns. Moreover, in the study of neuron systems, collective behaviour of a population of interacting neurons, namely, neuronal network, is a hot issue due to its importance to the processing and transmission of information. That is why, the interdisciplinary engagement of photonics with spike processing is fundamentally enabled by the strong analogy between the underlying physics biological neuron dynamics and lasers, both of which can be understood within the framework of dynamical systems theory. The high switching speeds, high communication bandwidth, and low cross talk achievable in optical domain are very well suited for an ultrafast spike-based information scheme with high interconnection network density. Delay coupled diode lasers system subjected to mutually optical injection, capable of studying the collective behaviour of the human brain neural networks system. In the proposed technique, each laser in the network has a different wavelength, various size, geometry and representing one neuron. This diversity can crucially influence the collective dynamical behaviour of the coupled system. The network status and the nonlinear threshold function required for
neural-network operation is achieved optically by interaction between the lasers. Coupled laser network show various dynamical regimes depending on the different type of coupling setup, light-matter interaction on various time scale involved and system control parameter chosen. So, N-coupled diode lasers, just equivalent to neural network system, is establishing a concept of collective interactions processing in the presence of delayed information transmission because human brain relies on the self-organized behaviour of networks of interacting, rather than isolated, neurons, giving rise to complex collective phenomena. However, before such concept can be considered for real applications,
fundamental nonlinear properties of coupled lasers network need to be understood.

APS March Meeting 2018, 2018

Coherence is one of the most curcial characteristic of any laser source for various range of appl... more Coherence is one of the most curcial characteristic of any laser source for various range of applications in modern imaging technologies. In this context, natural photonic structures are fascinating templates for biomimetic designs for novel optical systems, components or devices to control and manipulate light [1, 2]. While the direct use of natural biophotonic structures for optical applications is limited since they are composed of bio-polymers with rather poor mechanical and photo stability but the investigation of these structures allows both a better understanding of the host species evolutionary development and provide intriguing templates for biomimetic applications.
In this work, I demonstrate optical functionality of these photonic structures using ultrashort laser pulses as well as monochromatic CW illumination. Our observations directly demonstrate the coherent manipulation and control of light in these photonic systems and detail understanding of our observation could provide a platform for the development of novel photonic devices [1].
[1] P. Kumar et al., Laser Phys. Lett. (2015); http://dx.doi:10.1088/1612-2011/12/2/025901
[2] P. Kumar et al., Appl. Phys. Lett. (2014); http://dx.doi.org/10.1063/1.4865202

We numerically demonstrate the effect of optical injection induced modulation of the phase-amplit... more We numerically demonstrate the effect of optical injection induced modulation of the phase-amplitude coupling (factor α) on power spectra and optical characteristics in mutually coupled lasers system with finite delay. We observed the signature of tunable phase locked laser emission (coherent In-phase and Anti-phase) by directly controlling the non-linearity via manipulating phase-amplitude coupling. In addition, we predict the occurrence of frequency discretization and multistability near the phase transitions regimes, which could be useful in guiding the design of both experimental setup and compact photonic integrated practical devices for the generation of higher power laser system with the aid of optical phase control

Seeing inspiration from the nature, Optical physicists and Biologists have attracted much attenti... more Seeing inspiration from the nature, Optical physicists and Biologists have attracted much attention for doing collaborative research to find themselves simultaneously needing to provide fascinating templates for delivering increased performance and multi-functionality of optical components for chip scale integration. In addition, many different functions of biological materials and sculpture provide examples of how nature solves problems with tailored materials make them a rich source of inspiration for biomimetic applications. Technically, it is very difficult to develop a micro-optical components due to complicated fabrication process and other technical constraints on miniaturization. While the direct use of natural bio-photonic structures for optical applications is limited since they are composed of bio-polymers with rather poor mechanical and photo stability but the investigation of these structures allows both a better understanding of the host species evolutionary development and provide intriguing templates for biomimetic applications (reverse engineering) to enable production of novel photonic systems (efficient solar cell, micro-optical components) that perform similar tasks if mimicked. In this wok, we demonstrated optical functionality of complex microstructures organization on transparent insect wings surface using broadband ultrashort laser pulses as well as monochromatic CW illumination. Long range quasi-periodicity between these micro-structures arrays causes diffraction on various length scales, leading to complex intensity distributions. Our observations directly demonstrate the coherent interaction of light in these photonic systems and detail understanding of structural features (shape, size, arrangement, material) could provide a platform for the development of novel photonic devices for biomimetic applications. In addition, the existence of various symmetry in structural organization will be discussed.

We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-se... more We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-section quantum dash lasers emitting at ~1.55 µm and operating at ~21 GHz repetition rate, subjected to single and dual loop optical feedback into the gain section, over a wide range of feedback delay. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual-loop configurations. We demonstrate that dual-loop feedback with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, 10-50x better than single-loop feedback. In addition, for dual-loop configurations, under fully resonant conditions, phase noise is reduced to 295 fs [10 kHz-100 MHz], the RF linewidth narrows to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual-loop optical feedback with separate fine tuning of both external cavities is far superior to single-loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

ICTON2017, 2017

Nature has developed fascinating hierarchical arrangement of photonic micro-nano structures on va... more Nature has developed fascinating hierarchical arrangement of photonic micro-nano structures on various surfaces like plants, flowers, beetles, insect wings. Transparent insect wings in particular have not received much scientific attention that has been allocated to coloured wings, for example butterfly wings. Transparent insect wings surfaces have possessed microscopic mechanical and complex optical properties specifically tailored for the multi-functional purpose. While the direct use of natural bio-photonic structures for optical applications is limited since they are composed of bio-polymers with rather poor mechanical and photo stability but the investigation of these structures allows both a better understanding of the host species evolutionary development and provide intriguing templates for biomimetic applications (reverse engineering) to enable production of novel photonic systems that perform similar tasks. We have undertaken a detailed study of the transparency associated with many different insect wings.In recent study, we probed the natural quasi-ordered complex photonics structures on the transparent insect wings of rainfly (Termite) by a simple, non-invasive, real time transmission optical diffraction technique using monochromatic CW lasers and broadband femtosecond laser pulses. Our findings directly demonstrate how the diffraction pattern through the transparent insect wings is spatially and functionally correlated with its structural origination at various length scales. Our study account for the optical complexity inherent to real system,and allow bringing the system to a desired targeted state even when this state is not directly accessible due to constraints that limit the allowed intervention. Our observations directly demonstrate the coherent manipulation and control of light in these photonic systems anddetail understanding of our observation could provide a platform for the development of novel photonic devices for biomimetic technological applications.In my talk I will present a brief overview of coherent manipulation and control of light in the presence of medium with correlated disordered structural organisation.

Nature has developed hierarchically organized micro/nanostructures on the various insect wings su... more Nature has developed hierarchically organized micro/nanostructures on the various insect wings surfaces in a sophisticated manner to solve various technical problems related to material surfaces by combining the mechanical and optical functionalities for their survival. So, the best design fabrication of new materials performance depends on optimal morphologies exhibited at various length scales. Our experimental characterization techniques, which provide bio-mechanical and optical information about the morphologies of materials. Our observations offering new opportunities to understand not only how specific structures can form in materials but also how those structures relate to optical properties of interest. In addition, these studies has also contributed to the understanding of how progression of micro/nanostructure formation on various insect wings surfaces could aid evolutionary biologists investigating species adaptation to the various environmental conditions, as well as inform the debate on wing evolution.

Our multidisciplinary research interest crosses the borders of scientific disciplines which cover... more Our multidisciplinary research interest crosses the borders of scientific disciplines which cover various fundamental and applicative aspects in the field of ultrafast Laser physics and Nonlinear Photonics for paving the way towards Photonic Integration technology on chip scale. Particularly, we are working on generation and stabilization of ultrashort laser pulses via passive mode-locking using Quantum nanostructures based semiconductor lasers. Currently, we are dealing with optically -pumped Vertical- External Cavity Surface Emitting Laser (VECSELs) and Electrically pumped Quantum-dash laser subject to optical perturbation. In addition, we are also working on manipulation of spatial coherence of short laser pulses through Photonic structures for Optical Imaging and Biomimetic applications.

Light manipulation is crucial to enhance the light matter interaction in micro/ Nano photonic str... more Light manipulation is crucial to enhance the light matter interaction in micro/ Nano photonic structures by generating desirable optical field components and increasing time and pathways of light propagation through the photonic structures. However , controlling the femtosecond laser pulses with nanometer accuracy is very challenging, as the limitation imposed by dispersion on the pulse duration and by the diffraction on the focusing of light must be overcome simultaneously. Thus, ultrashort laser pulses exhibit an interdependence of temporal and spatial coordinates, referred to as spatio-temporal coupling. Nature has developed a broad range of remarkable photonic architectures on the various insect wings surfaces to possess various optical properties for the multifunctional purpose. However, before such concept can be consider for real life implementation, fundamental optical properties or optical effects of these photonic systems need to be understood. Seeing inspiration from nature, we have naturally found deeply grooved blazed micro-grating arrays on transparent insect wing (Rain-fly) surfaces to manipulate and control light for tunable optical functionality. Our observation may open up new opportunities in biomimetic device research and also have potential for the design and development of diffractive optical components for photonic integrated system .

Quantum nanostructure-based mode-locked (ML) dual-section semiconductor lasers have received much... more Quantum nanostructure-based mode-locked (ML) dual-section semiconductor lasers have received much attention in recent years due to their potential applications in high-speed optical telecommunications and clocking. Particularly, passively mode-locked lasers subject to optical feedback or optical injection possess a rich diversity of dynamical regimes including lasing wavelength bistability, dropout dynamics and dark pulses due to their broadband gain and fast carrier dynamics. These processes are characterized by a large number of quite different characteristic time scales, which determine the quality of mode-locked pulses and the dynamical behavior of the laser in general. Instabilities need to be identified and studied, with a view to their suppression and exploitation in telecommunication networks. In this work, we present experimental studies of complex nonlinear dynamics in mode-locked quantum-dash lasers subject to frequency dependent optical feedback with fixed filtering. Filtered or dispersive optical feedback offers advantages over conventional optical feedback as its provides specific controllable spectral content of feedback to manipulate the laser dynamics, specifically by varying the filter bandwidth and detuning from the free running mode-locked frequency, without introducing attenuating optics in the feedback loop. In addition, we discuss how the various dynamical regimes of the mode-locked laser with filtered optical feedback depend on the filter bandwidth and frequency and also how the presence of particular dynamical states can induce a significant change in the timing jitter of a mode-locked pulse train. We suggest that the dynamics are manipulated and controlled by changes in phase-amplitude coupling, and thus strong carrier dependence of the index on carrier density and varying with dispersive optical feedback. Physically, when the free running mode-locking frequency is on the blue side of the filter center frequency then the feedback induces a red-shift in frequency with reduced phase-amplitude coupling factor α. Our technique provides a simple and low cost way to effectively control the Rf dynamics of the mode-locked laser diode and here its uses as an optical clock, lidar or frequency comb.

A major advantage of FOF is that they can produce chaotic emission of narrow bandwidth, which cou... more A major advantage of FOF is that they can produce chaotic emission of narrow bandwidth, which could reduce the synchronization degradation. So dynamical complexity could be manipulated by filter characteristics. The filter width and the detuning between the central frequency of the filter and the solitary laser frequency strongly influence the dynamics of the laser and the system exhibits different opportunities of control as a additional key to improve the security in the communications. Adjusting filter bandwidth allows tuning of characteristics time scale while feedback strength and delay time control the complexity of the dynamics

We probe the interaction of monochromatic CW and broadband ultrashort fs laser pulses with quasi-... more We probe the interaction of monochromatic CW and broadband ultrashort fs laser pulses with quasi-periodic
bio-photonic structures on transparent insect wings using diffractive optical technique. We find the coherent
manipulation and control of light in the presence of optimal correlated noise in the structural organization. A
comprehensive analysis of the observed asymmetric far-field diffraction pattern unveiled the modulation in
spatial coherence of the incident laser pulse as well as detailed information of the structural correlation at various length scales.

A systematic investigation of ML (mode-locking) trends versus operating conditions was carried ou... more A systematic investigation of ML (mode-locking) trends versus operating conditions was carried out. The simultaneous effects of gain current and absorber bias on the pulse duration
and the FWHM of the RF spectrum with the optical feedback and without feedback.

We probe the natural quasi-ordered complex photonics structures on the transparent insect wings ... more We probe the natural quasi-ordered complex photonics structures on the transparent insect
wings by a simple, non-invasive, real time transmission optical diffraction technique using
monochromatic CW lasers and broadband femtosecond laser pulses. Our findings directly
demonstrate how the diffraction pattern through the transparent insect wings is spatially and
functionally correlated with its structural origination at various length scales. In addition, we
investigate various complex nonlinear dynamical instabilities including zero-lag
synchronization (ZLS) between delay-coupled diode lasers system subjected to mutual
optical injection in a face-to-face configuration. The fundamental properties of the coupled
system are that perturbation to one component can affect other components, potentially
causing the entire system to change behaviour. Our study account for the optical complexity
inherent to real system, and allow bringing the system to a desired targeted state even when
this state is not directly accessible due to constraints that limit the allowed intervention. Our
observations directly demonstrate the coherent manipulation and control of light in spatial
and temporal domain in these photonic systems in order to pave the way for the realization of
complex integrated circuit on the chip scale.

We experimentally and numerically probe the spatiotemporal optical complexity with two different... more We experimentally and numerically probe the
spatiotemporal optical complexity with two different photonic
test-bed: delay-coupled diode lasers system and quasi-ordered
natural photonic structures in the transparent insect wings. Our
findings directly demonstrate the coherent manipulation and
control of light in spatial and temporal domain in these photonic
systems for the realization of complex integrated circuit on the
chip scale.
I

"A broad range of gorgeous biological photonic architectures have been found that manipulate ligh... more "A broad range of gorgeous biological photonic architectures have been found that manipulate light such as vivid colors displayed by butterfly wings, various insects, peacock feathers, fishes etc. Since these natural biophotonic architectures are hierarchically arranged on various length scales these invariably result in complex optical phenomena that have been evolved and optimized over millions of years of natural evolution. These complex optical effects and their functional role have intrigued scientists, yet knowledge of how light behaves within these structures has not been fully understood. Many discoveries have revealed biological system designs that have evolved and existed naturally and that were, until their discovery in nature, thought to have been the recent product of technological innovation.

In this book we discuss formation, mechanisms and functional applications of diverse complex optical phenomenon observed in the eyes, wings, and exoskeleton of various insects and animals such as in butterfly, beetles, fly, fish, birds etc. These complex optical effects include structural colors, polarization sensitivity, spectral filtering, broadband anti-reflection coatings for various functions. We shall also discuss our recent finding where we have been able to map the so-called photonic architecture in transparent insect wings exploiting optical diffraction technique that reveals new insight into the long range correlation and symmetry of their microscopic arrangements. These remarkable optical phenomena have lead to several technological optical applications, novel multifunctional solutions to challenging problems and optimizations of existing optical devices. This area of contemporary biophotonic research is very fertile and promising for many new developments in the future. While the subject has its origins in the optical physics, it has broad significance and applicability in other disciplines such as engineering, chemistry, biology, physics and material science. However, the greatest challenge to the further development of this field is in the reliable and inexpensive synthesis of the optical materials and self-assembly in desired architecture and length scale. This book will offer a compiled knowledge in this field at one place, contemporary research topics and technological optical applications with future challenges. Therefore we believe that it will serve as key reference for the further development and application of biophotonic architectures.

Book will be organised as follows. We shall beginning with an introductory overview of diverse natural biological photonic structures. We shall describe the photonic architecture in the eye- system of various insects, its spectral and polarization sensitivity, and functions. We shall then present a comprehensive survey of the optical phenomenon first in reflective photonic architectures mostly in butterfly and then in transparent insect wings. The focus will be to understand how the short and long range order at appropriate scale interact with the wavelength of light to provide various complex phenomenon such as iridescence, color mixing effect, polarization sensitivity, optical diffraction and interference etc. We then turn to the material synthesis and their genetic control for such multi-scale, self-organized and hierarchical architectures. The natural design criterion will be compared with the artificial approaches to mimic the optical phenomenon. Finally we shall present a summary of optical technologies motivated by these natural biophotonic architectures. We shall end our book by presenting key challenges in this area that might be crucial to develop novel hierarchical self assembled green material as well as new device applications."

Natural Photonic structures on Insect wings : Light manipulation and control for enabling future ... more Natural Photonic structures on Insect wings : Light manipulation and control for enabling future optical technologies on chip scales via exploitation the combined effect of spatial structural correlation and optical coherence in the interaction.

It is showing that coherent interaction of short pulse and CW laser with photonic structures dict... more It is showing that coherent interaction of short pulse and CW laser with photonic structures dictate the role of optical coherence and structural arrangement for the manipulation and control light.—Pramod Kumar, Optoelectronics & Nonlinear Optics Lab. Department of Physics/Tyndall National Institute, Kane Building, University College Cork (UCC) Western Road, Cork, Ireland

Quantum technologies which enable to tackle problems which are hard or even impossible to solve b... more Quantum technologies which enable to tackle problems which are hard or even impossible to solve by classical computers due to time complexity. Scientists continue to seek more efficient optical platform for solving time demanding problems such as combinatorial optimization and Prime factorization problems in the reduced execution times. Moreover, we are living in the modern technology information age and every information needs to be secured from unauthorized access. So, ever increasing demand of highly secure communications or secure data transmission for example, online banking, Internet privacy, protecting credit card numbers, medical records, and other confidential information, is the long standing issue as every type of information and transaction is available through internet. More specifically, some cryptographic algorithms such as RSA critically depends on the fact that the terrible difficulty for finding the prime factorization of large integer. That why prime numbers makes them so special in cryptography. In short, integer factorization is hard in the sense of computational efficiency as RSA-2048, for example, would take one billion years with a classical computer. A quantum computer cold do it in few seconds. So one can crack RSA if we can find a miraculous way to find prime factor of large integer. In this regards, Alan Shor came up with an idea about converting the problem of finding prime factorization into order finding problem of a function. Shor's algorithm performs factoring of large integers, though it is not just a single-step operation as described. The algorithm consists of both quantum and classical processing. The classical part makes use of a result from number theory to find a factor of by using greatest common divisor. So, just one of the step of the Shor's algorithm need to be implemented on a quantum computer, while the rest can be done on a classical super computer. This paradigmatic algorithm stimulated the flourishing research in quantum information processing and the quest for an actual implementation of a quantum computer. Over the last decade, using some optimizations, several instances of a Shor algorithm have been implemented on various platforms and clearly showed the feasibility of quantum factoring. Superposition, entanglement and interference are the main characteristics of quantum world that make quantum computation faster solving of certain problem that require exponential computing time with classical computer. Scalability and efficiency are the crucial issues to be solved using some desirable optical technique. In this, I will discuss some open questions and problems for current and upcoming realizations of Shor's algorithm, which also apply to several other largescale quantum algorithms of interest.

Invited Lecture at Imperial College London, 2018

The semiconductor diode lasers are known to be very sensitive to the external optical perturbatio... more The semiconductor diode lasers are known to be very sensitive to the external optical perturbations such as, for example, optical self-feedback, optoelectronic feedback, optical injection due to phase-amplitude coupling factor alpha, α. Therefore, mutually delay-coupled semiconductor lasers in a face-to-face configuration show a plethora of dynamical complexity in the emitted radiation that make them ideal candidate for fundamental studies of coupled oscillators as well as for practical applications ranging from optical communications to computing. On the one hand these dynamical instabilities are undesired features and disturb the many applications where one needs the constant stable power but on the other hand they may allow for new methods for secure communications using chaos synchronization. The variety of optical complexity in these system which we have investigated theoretically as well as experimentally are well behaving, well understandable, well classifiable in terms of complex nonlinear dynamics.

The fundamental properties of the coupled system are that perturbation to one component can affect other components, potentially causing the entire system to change the collective behaviour. Our study account for the optical complexity Inherent to real system, and allow bringing the system to a desired targeted state even when this state is not directly accessible due to constraints that limit the allowed intervention. So the systematic study and control of these nonlinear dynamics provides fundamental insight into the underlying physics of the system. On the basis of which one can redesign the device in order to stabilize the working point against environmental fluctuations or improve the processing, or simply exploit the dynamical performance of a system to one’s advantages.

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we know of problems that are believed to be hard for classical computers, but for which quantum a... more we know of problems that are believed to be hard for classical computers, but for which quantum algorithms have been discovered that could solve these problems easily. But perhaps the most persuasive argument we have that quantum computing is powerful is simply that we don't know how to simulate a quantum computer using a classical computer; that remains true even after many decades of effort by physicists to find better ways to simulate quantum systems. Now, we have at least few good reasons for thinking that Quantum algorithm for classically intractable problemshave capabilities surpassing what classical computers can do.The best known example is the problem of finding the prime factors of a large composite integer. We believe factoring is hard because many smart people have tried for many decades to find better factoring algorithms and haven't succeeded. Perhaps a fast classical factoring algorithm will be discovered in the future, but that would be a big surprise. Finding the prime factors of a given integer N is a problem that requires super-polynomial time for conventional digital computers. A polynomial-time algorithm was invented by Shor for quantum computers. Is there any optical system able to compute such a factoring algorithm? Optical systems are perhaps the most robust and fastest accessible system capable of dealing Shor's function. Many other systems, like ion trap, superconductors, NMR, will achieve it at very low temperature or very high vacuum. In this work, we present numerical and experimental observations that demonstrate prime factorization using optical diffraction but without quantum entanglement. Prime factorization includes three major steps. First, a classical computer calculates the sequence of numbers a x mod(N), where N is the number to be factorized, a is the randomly chosen positive integer, and x = 1, 2, 3, 4, 5, 6….N-1. Next, the period of the calculated sequence r is determined by exploiting optical diffraction. Finally, making the post processing by the computer determines the primes based on the obtained r. A system for prime factorization with optical modulo operations is developed and demonstrated. The experiment for period finding was conducted on a Digital Micro mirror device (DMD). We chose number 33 for testing and determined its primes using a sequence of measurements. Scalability is one of the major strengths inherent in this type of DMD device, which may provide a route to find primes of large integer. We discuss the physical and technological limitations of this approach, which define the maximum size of N and the computational speed. Although this classical approach cannot compete with the quantum algorithm in terms of efficiency, quantum entanglement can potentially be used as aimed at speeding up prime factorization for classical computers. Numerically, in the proposed method, optical Fourier transform is considered to be useful in prime factorization. Basic concept of this method is shown in this report. And, improvement for our method is proposed based on the discussion. With the constructed system, effective results can be obtained using the proposed method. We show how this factorization algorithm can emerge from optical diffraction of computer generated binary grating and we present a number of simple implementations in optics.Moreover, wwe will provide a detailed description and simulation of the algorithm using MATLAB. Precursory information regarding quantum phenomena such as superposition, entanglement, and Dirac notation, will be described in great detail so that the reader may have a better understanding of the operations in Shor's algorithm.