Professor, Dept. of Electronics & Communication at Malaviya National Institute of Technology Jaipur
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Author
Area of Expertise:
Optical switches, couplers, spitters, logic gates and circuits ,
Integrated Photonics ,
Microring resonator based optical devices and systems ,
Non linear characteristics of Photonic Crystal Fibers ,
Nano Photonics ,
Photonic Biosensors
Prof. (Dr.) Ghanshyam Singh, an recipient of Distinguished Lecturer Award from IEEE Photonics Society for term 2017-18, has received B. Tech. degree in Electronics and Communication Engineering from NIT Silchar (then REC Silchar), M. Tech. and PhD degrees in Electronics and Communication Engineering from Malaviya National Institute of Technology (MNIT) Jaipur. In early 1999, he joined the academic staff of MNIT Jaipur, where he is a Professor with the Department of EC Engineering. He had worked as visiting research scholar/visiting professor in the area of Photonic Switching and Networks for various periods at the Department of Physics, Heriot Watt University, Edinburgh, UK (March 2009), the Institute of Photonics, University of Eastern Finland, Joensuu, Finland (2010) under the CIMO Fellowship (Govt. of Finland) and Department of EEE, Keio University, Hiyoshi Campus, Yokohama, Japan (October 2013). Dr. Singh has extensive teaching, research and sponsored R&D experience on many aspects of Optical Communication and Photonics Technologies and has published/reported over 150 research papers/review articles in peer reviewed International journals/ conferences. He has delivered expert talks on related research topics during various events held in India and abroad (including Germany, Finland, UK, Singapore, Japan, Hong Kong, Ukraine, Belarus, China, Australia, Malaysia, Poland, Italy, France, Spain, Portugal and USA). Dr. Singh is a senior member of SPIE, OSA, IEEE and Fellow of OSI and IETE and member of ISTE, IE (India), etc. Presently, Dr. Singh has done joint projects with partner researchers from Keio University (Japan), University of Vienna (Austria), LNPU Lviv (Ukraine) and Cairo University (Egypt) and Presently engaged with researchers from Russia, South Africa and China. His current research interest includes Micro and Nano-structured Photonic Devices, Photonic Crystal Fibers, Integrated Photonics, Photonics Sensors, AI applications in Photonics, etc.
Publications (21)
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This work reports results of laser beam profile measurements, performed for earlier on designed and successfully fabricated silica few-mode microstructured optical fiber (MOF) with hollow-GeO2-doped-ring core (HRC). We compared two drawn from the same preform HRC MOF samples without and with induced during the drawing process twisting of 790 revolutions per meter. Researched silica HRC MOF with outer diameter 65 µm contains hollow ring-core inner diameter of 30.5 µm with wall thickness of 1.7 µm and refractive index difference Δn = 0.03; 90 air holes, placed over typical hexagonal geometry in the periphery domain from the outside HRC at the distance 14 µm, with hole averaged diameter 2.5 µm and pitch 7.5 µm. According to simulation results (mode analysis, performed by rigorous finite element method via commercially available software COMSOL Multiphysics®), it supports two guided LP-modes (fundamental LP01 and the first higher-order LP11) or 4 HE/EH odd and even eigenmodes – HE11/EH11 and HE21/EH21, respectively. We present some results of laser beam profile measurements, performed under various launching conditions (different laser sources as well as excited optical fibers (both commercially available single-mode optical fiber of ITU-T Rec. G.652 and multimode optical fiber 50/125 of ISO/IEC Cat. OM2+/OM3)) at the output ends of researched HRC MOF twisted and untwisted samples as well as at the output end of large core multimode optical fiber 100/125, aligned with excited HRC MOF.
This work reports comparative results of mode analysis, performed for earlier on designed silica microstructured optical fiber with ideal equiangular spiral six-ray geometry (ESSR-MOF) and for its real fabricated sample, differing from the model by weak asymmetry and deformed air holes. We discuss issues of input data preparation to specify analyzed complicated non-ideal fiber optic structure for computation by using rigorous finite-element method. Some results of the comparison between mode field patterns as well as guided mode effective refractive index spectral characteristics are represented. It is demonstrated, that potential deviations from the desired MOF geometry, occurring due to features of silica MOF fabrication technological process, should be taken into account during the design to predict real values of mode parameters for manufactured MOF.
All-optical computing has drawn increased interest from researchers in recent years to meet the need for fast optical signal processing. This paper demonstrates the design of an all-optical CNOT logic gate using a silicon nitride (Si3N4) based optical ring resonator (ORR). Two optical ring resonators have been employed to design the CNOT logic gate. The simulation results obtained from MATLAB using the mathematical equations of the ring resonator validates the proposed CNOT logic gate. The proposed CNOT logic gate is compact and elementary.
This work intends to present various Photonic Crystal fibers (PCF) for the propagation of orbital angular momentum(OAM) modes. Hexagonal, spiral and octagonal-shaped fibers are designed for the observation of OAM modes. The proposed fiber designs have shown high purity of nearly 90% and has proved that the hexagonal design has the highest mode confinement. The finite element method is employed to obtain 12 OAM modes at the operating wavelength of 1.55 μm.
This work presents results of mode analysis and dispersion spectral characteristic computation, performed for recently presented successfully fabricated silica few-mode microstructured optical fiber (MOF) with hollow-GeO2-doped-ring core (HRC). Here, we utilized manufactured HRC MOF end face photo image to get averaged parameters for input data. Therefore, following simplified model HRC MOF was simulated and researched: it has outer diameter 67 µm; inner diameter of hollow ring-core is 10 µm, wall thickness 4 µm and refractive index difference Δn = 0.030 (percent of GeO2 dopant is about 20.5 mol%); 90 air holes, placed over typical hexagonal geometry in the periphery region with averaged diameter 1.85 µm and pitch 3.9 µm. According to simulation results (mode analysis, performed by rigorous finite element method via commercially available software COMSOL Multiphysics® 6.1), modeled HRC MOF provides two guided LP-modes (fundamental LP01 and the first higher-order LP11) or 4 HE/EH odd and even eigenmodes – HE11/EH11 and HE21/EH21, respectively: therefore, two orbital angular momentum (OAM) modes (OAM11 and OAM21) are localized and supported by the researched and simulated HRC MOF design. In this work we present results of spectral characteristics, computed for mode effective refractive indexes as well as for mode group delays and chromatic dispersion parameters, calculated both for eigen and OAM modes.
Earlier on we introduced model of piece-wise regular fiber optic link, operating in a few-mode regime: laser-based data transmission over large core optical fiber. Presented model is based on piecewise regular representation with general approach of split-step method application. It allows to take into account laser-excited optical signal launching conditions, differential mode delay, differential mode attenuation, higher-order mode chromatic dispersion and mode mixing / power diffusion, occurring due to optical fiber irregularity and fiber optic cable bends / twisting / stress / tension. While optical fiber irregularity can be directly set by protocols of optical fiber outer diameter monitoring system of drawing tower, cable external mechanical influences are simulated via equivalent angular misalignment at the splices of regular spans. Therefore, this work is concerned with issues of selection of this equivalent angular misalignment (EAM). We performed a computational test series under various values of mentioned above EAM under following comparison with experimentally measurements of few-mode optical pulse responses at the output of multimode optical fibers with strong differential mode delay effect.
The current research proposes the development of a plasmonic elliptical ring resonator structure with a Metal (Ag) Insulator Metal (Ag) waveguide configuration for the purpose of bio sensing. The research involves a distinctive exploration of the sensitivity and peak resonance wavelength, which are found to be varied by altering the aspect ratio of the elliptical ring resonator. The results reveal a marked increase in sensitivity, ranging from 732.60 nm/RIU to 1113.70nm/RIU, by changing the aspect ratio (ratio of major to minor radius of elliptical ring resonator) from 1.61 to 3.72. Furthermore, these adjustments produce a noticeable redshift in the peak resonance wavelength, as the aspect ratio increases. The study also highlights the impact of other geometrical factors of the sensor on its sensing characteristics. It is found that sensitivity changes significantly with the change in width of resonator and linear waveguide, and it is found to be decreased when width increases. The results of variation in width of waveguides reveals that there occurs a red shift in resonance wavelength when width decrease and vice versa. Based on the finding of all significant geometrical factors an optimized structure is selected with the optimum value of sensitivity. Which evidences its suitability for biosensing purpose and with its superior capabilities, the sensor can play a crucial role in distinguishing between healthy and cancerous cell and will be helpful in detecting cancer at early stage. The investigation and observations involved in the process are computed numerically using the finite difference in time domain method (FDTD).
The current work proposes an optimized design for 2-bit synchronous up counter using silicon nitride on insulator optical microring resonators (MRRs). The research involves exploring the existing designs of up counter structures based on MRRs, and then minimizing the number of rings being used in the proposed model. The proposed design uses four MRRs for Synchronous up counter operation and the model has been validated through the MATLAB simulation result. The main component of the design is the MRR which can act as a switch depending upon the output at the drop port or the through port according to the MRR being in an on-resonance or off-resonance state respectively. The principle of the MRR is that on applying a vertical pump signal over the ring, the non-linear refractive index of the ring undergoes a temporary blue shift resulting due to π- phase shift in the ring, changing the resonant frequency of operation of the ring. The average pump power required for the blue shift can be obtained from the phase shift vs. the average pump power graph simulated in MATLAB. This shift in resonance frequency is employed to switching action for the signal to be output at the drop port or the through port of the MRR and based on the drive signal inputs of the present state and the clock to the rings in the resonator structure which act as pump signal over the ring, the next state of the counter is determined.
KEYWORDS: Signal to noise ratio, Free space optics, Receivers, Turbulence, Transmitters, Telecommunications, Modulation, Laser sources, Systems modeling, Forward error correction
In free space optical communication (FSO) communication, it is assumed that the fading due to atmosphere turbulence (AT) is uncorrelated at the receiver. But, in practice the spacing between the receivers is less than the fading correlation length. So, we have to consider a correlated statistical model for FSO AT model. In this paper, we have analyzed space shift keying (SSK) modulation scheme over correlated Gamma-Gamma (GG) fading model. We have derived an average bit error rate (ABER) using moment generating function (MGF) for space shift keying modulation scheme over correlated Gamma-Gamma (GG) fading model. The system is analyzed for different atmospheric conditions, correlation values and different number of receivers. It can be observed that as we increase the correlation value, the ABER value deteriorates. It can be observed that the ABER does not depend on turbulence at low SNR, but for high SNR the ABER performance improves and the ABER performance is approximate same in weak and moderate turbulence. However, the difference of SNR between moderate and strong turbulence is approximate 5 dB for ABER value of 10−4. We note that at a given SNR, the ABER improves as we increase the number of receivers. Also, it can be observed that the ABER deteriorates as correlation increases for same number of receivers. We have also analyzed the system both uncoded and LDPC coded SSK transmitter systems. It is observed that for ABER value of 10−4, the SNR difference between LDPC coding and without encoding is approximate 3 dB.
KEYWORDS: Spatial light modulators, Orthogonal frequency division multiplexing, Transmitters, Modulation, Signal detection, Data transmission, Receivers, Wireless communications, Systems modeling, Telecommunications
Optical Wireless Communication (OWC) has the potential to offer a transmission link that is both dynamic and flexible in comparison to fiber optics communication. The optical spectrum exhibits a significantly greater range than the conventional Radio Frequency (RF) communication spectrum. Optical Orthogonal Frequency Division Multiplexing (OOFDM) can be treated as an integral part of OWC Systems. It is a modulation technique which refers to the implementation of OFDM in the Optical Domain. For the OFDM signal to be transmitted in the Optical domain, we perform Intensity Modulation/Direct Detection and for that the signal needs to be real and positive. In this paper, we have made the signal Hermitian symmetric along with IFFT and performed adaptive biasing to make the transmitting signal real and positive respectively. One of the major issues which still persists is the high Peak-to-Average Power Ratio (PAPR). To overcome this, we have implemented Selected Mapping (SLM), using Shapiro-Rudin Phase Sequences (SRPS). We have used SRPS as they yield a low crest factor, have good randomness, strong correlation, and help in reducing the average transmit power, which will eventually help in decreasing the complexity of the system. By performing Adaptively Biased Optical OFDM (ABO-OFDM) in conjugation with SLM we have been able to achieve a reduction of about 3 dB in the PAPR graph, without affecting the BER curve. Moreover, the increase in the system complexity is comparatively lower, or it can be stated that the increase is approximately halved.
This work presents some results of pulse and spectral responses, performed for laser-excited pilot sample of earlier on designed and fabricated chiral silica few-mode optical fiber (FMF) with induced twisting 66 revolutions per meter (rpm), typical (for telecommunication optical fibers) cladding diameter 125 μm, weakly increased core diameter up to 11 μm and numerical aperture NA=0.22, corresponding to improved height of quasi-step refractive index profile. Described FMF 11/125 provides propagation of 4 and 6 guided modes over “C” and “O”-bands, respectively. We present results of tests, focused on researches of few-mode effects, occurring under laser-excited optical signal propagation over pilot sample optical fiber, and their influence on pulse and spectral responses, including some measurements, performed for fiber Bragg grating, recorded in tested FMF 11/125.
This work reports the results of bandwidth measurements and tests, performed for earlier on designed and fabricated pilot lengths of new silica laser-optimized graded-index multimode fibers (LOMFs) with extremely enlarged core diameter up to 100 μm and "typical" "telecommunication" cladding diameter 125 μm. Presented optical fibers are targeted for harsh environment short-range multi-Gigabit onboard cable systems and industrial networks. Proposed LOMF 100/125 differs by specially optimized graded refractive index profile, that provides low differential mode delay (DMD) for selected guided modes. We present some results of tests, performed for fabricated pilot 520 m length of described LOMF 100/125, focused on researches of bandwidth features. They contain DMD map and transfer function measurement as well as 10GBase-LX/SX channels eye-diagram and bit-error-ratio reports with following direct detection of the maximal acceptable optical fiber length for guaranteed 10Gbps channel supporting.
A flat Nano-metallic (Silver) surface plasmonic lens for wider optical wavelength operation based on the phase and
amplitude modulation by tuning the slit widths is introduced. The design novelty lies on its complex structure with the
macro-parameters such as focal length with freedoms in its material profile, thickness, slit width and the pitch. A
simplified implementation of the Nano-metallic lens with equidistant slits but bearing different widths is evaluated using the finite difference time domain method. The design tolerance and variation in the focal point position in accordance to alteration in the properties of the lens are explored in brief.
When a patch antenna is fabricated, dimensions of the patch may be slightly different from the designed values due to tolerances in the fabrication process. This alters the resonance frequency of the antenna. To overcome this problem this paper presents a new design approach for fine tuning the resonance frequency by dielectric constant engineering. This approach is especially suited to low temperature co-fired ceramic (LTCC) and similar processes where the antenna dielectric is composed of several layers. Composite dielectric constant of this multilayer structure is altered in such a way that the resonant frequency is set back to the designed value. It has been verified that for proposed micro strip antenna (MSA) design, the frequency-area curve follows a quadratic relation with a variable R (Ratio of cavity area to the patch area). This mathematical model is true up to R 1.27. After this saturation effects set in and the curve follows a straight line behavior.≡
Novel index-guiding photonic crystal fibers (PCF) with rings of cladding holes (circularly or elliptically shaped) arranged in the Fibonacci series are proposed. The dispersion, confinement losses, and generated birefringence in PCFs are evaluated for light signal at 1.55-µm wavelength, by employing alterations in various design parameters. Full-vector analysis using anisotropic perfectly matched layers is performed to validate the accuracy of the modeled PCFs in a finite-difference time-domain environment. For such PCF modeling, the lower value of dispersion is found to be 7.311 ps nm−1 km−1, and the zero-dispersion wavelength is shifted to lower infrared region in accordance with variation in the hole diameter-to-pitch ratio.
Modeling and detailed performance analysis is carried out to realize a multimode interferometer optical switch by inserting an appropriate image-modulated (IM) region. The concept of self-imaging characteristics of multimode waveguides has been utilized in order to drive the designed device as a photonic switch. Transition losses in the waveguides of the structure are maintained at low levels by selecting appropriate dimensions to increase overall performance of the switch. It has been observed that by inserting an additional IM region, switching losses and corresponding crosstalk levels can be reduced significantly. The device performance is checked for a wider range of index variation in the IM region with respect to other regions for a test wavelengh of 1.55 µm. With rigorous and repetitive simulation, a crosstalk level better than -22.2 dB for either case of polarization state (transverse electric and transverse magnetic) of input has been achieved. The design also possesses a design tolerance in the range of ±0.25 to ±0.5 μm, within which variation in the imaging length and its subsequent adverse effects on device performance remains less than 1.5%.
Modelling of a compact and completely non-blocking 4×4 optical switch utilizing integrated multi-mode interference (MMI) waveguides with a channel profile of Ti-indiffused Lithium Niobate is described. Design novelty lies in its satisfactory operation for two wide optical windows (100 nm each), with center wavelengths (λcentre) of 1.3 and 1.55 µm, possessing low losses. For either of these windows, the average value of propagation losses are maintained lower than 1 dB with a vacillation of extremely low polarization dependent losses ( ≤ 0.15 dB). Index tuned regions are optimized to achieve average crosstalk levels better than −19 and −12 dB for its operation in the wavelength range of 1.25 to 1.35 µm and 1.50 to 1.60 µm, respectively. It is also observed that switch possess absolute loss uniformity (of the range of 0.5% to 1.6%) with a maximum of ±2.5% tolerance in the structural parameters.
This paper describes the modeling of a 2×2 multimode interference (MMI) switch, with a channel profile of
Titanium indiffused Lithium Niobate. Design novelty lies in its satisfactory operation for two wide optical
windows (100nm each with centre wavelengths, λcentre of 1.3 μm and 1.55 μm) with low switching losses and
crosstalk levels. Index tuned regions are optimized to achieve crosstalk levels of ≥ -18 dB and ≥ -14 dB for its
operation in the wavelength range of 1.25 μm - 1.35 μm and 1.50 μm - 1.60 μm respectively. For either of
these wavelength ranges, the switch losses (excess and insertion losses) are maintained lower than 1 dB.
A diffusion process controlled modelling of Titanium-indiffused Lithium Niobate (Ti: LiNbO3) channel waveguides
(of μm dimension) for Machzehnder Interferometer (MZI) switch has been presented. The effect of various
indiffusion process parameters e.g. dopant strip thickness, lateral and vertical diffusion length on the insertion loss has
been taken care of, to reduce the switch losses. Transition losses in the curved waveguides of the structure are also
minimized by selecting low loss bend structures to increase overall performance of the switch. The computed results
for switch performance are in good agreement with the published data.
This paper reviews the development of hydrogen silsesquioxane nanostructures (sub-100nm) on a silicon platform.
The effect of HSQ resist in thick (128nm thick resist) and thinner state (30nm thick resist) has been demonstrated and
minimum possible structures with these are discussed in details. Most applicable structures like straight lines/spaces,
sharp joints/corners and dots were developed to investigate the effects of development time on the lithography
properties of HSQ. Soft bake after spinning process had been avoided in view of achieving better contrast and stable
resist deposition. We had also reached to a conclusion that increasing the development time could improve resist
contrast and pattern resolutions up to certain limits but may vary with type of structures and other conditions.
In this paper, design of an all-optical switch using MZI switching elements with SOA's and its works performance is
explained. The effect of variations of output power with respect to control signal wavelength, data signal power and control
signal power are examined and plotted. Also the optical spectrum and time domain analysis has been done to demonstrate its
operational features.
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