R. K. Sinha received M. Sc. degree in physics from the Indian Institute of Technology (IIT), Kharagpur, India, in 1984, and Ph.D. degree in Fiber optics and Optical communication from the IIT, Delhi, India, in 1990. During 1989–1991, he was a Postdoctoral Research Student at Osaka University for Foreign Studies, Osaka, Japan, and Electronics Engineering Department, Kobe University, Japan. He has also held visiting scientist appointments at ICTP-Italy in 1991 and the University of Campinas, Brazil in the year 1995. He had been an academic visitor to leading university of the world which includes, MIT, Harvard, Stanford, Boston, Cambridge, Glasgow, Southampton, Bath, London, Kobe, Osaka, Tokyo, Hokkaido, Singapore, National Tsing Hua University, NTU Taiwan and EPFL Switzerland, etc. for research collaboration, delivering seminar/invited lectures. He had held various research and academic positions at the Indian Institute of Science (IISc), Bangalore, BITS Pilani and REC (now NIT) Hamirpur during 1991-1998.He has served as a Director of CSIR-Central Scientific Instruments Organisation (CSIO) Chandigarh, CSIR-CEERI Pilani, and CSIR-IMTECH. Currently, he is a Professor of Applied Physics Department & Chief Coordinator of TIFAC–Centre of Relevance and Excellence (CORE) in Fiber Optics and Optical Communication at Delhi Technological university (Formerly known as Delhi College of Engineering, University of Delhi), Delhi. He has also served as Head-Applied Physics, Dean(IRD) and Dean ( Academics) of DCE and DTU Delhi. He is the author or co-author of more than 350 research publications in Journals and Conference Proceedings. He has supervised 18 Ph.D. thesis and over 22 R&D sponsored projects and mentored for 39 technologies transfer. Prof. R. K. Sinha has been awarded several national and international awards and fellowships for his research work in the area of optics and photonics. His current research interests are Photonic Crystal and Metamaterial-based Devices.
Publications (81)
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The proposed work presents the design of a photonic crystal structure based on silicon with a square lattice arrangement. It probes the effect of pressure variation on the photonic bandgap and midgap wavelength of the structure. The photonic crystal structure shows a bandgap for the TM mode. The variation in the refractive index of silicon with pressure is utilized to study the bandgap characteristics of the structure with a change in applied pressure. It is observed that the midgap wavelength varies linearly with variations in pressure. This linear variation indicates the application of the proposed structure as a pressure sensor.
Metalenses have shown their great ability in efficient manipulation of light fields and have been proposed for variety of devices with specific functionalities making the world more compact and flatter. However, a high meta-atom aspect ratio is still a drawback as it causes difficulty in fabrication of metalens. In this paper, we propose a design principle to lower the meta-atom aspect ratio in near infrared region. The designed metalens is made by arranging hollow cylindrical nanopillars made up of crystalline Silicon and the substrate is of material SiO2. The simulation results show that the required aspect ratio of our design is much smaller than that of solid single material meta-atom thus without compromising with the transmission efficiency of the meta-atom. Also, the designed metalens have a high focusing efficiency of nearly 90% and with polarization independent characteristics. Our proposed design may pave the way towards easier fabrication and thus application of near infrared devices.
In this paper, we report the design and analysis of a metamaterial for multiband microwave applications with epsilon negative (ENG), mu-negative (MNG), and negative effective refractive index characteristics. The suggested metamaterial comprises a 0.16 cm thick FR-4 substrate with a unit cell dimension of 1 cm × 1 cm. Design and simulation of the proposed metamaterial structure are performed with the Finite element method using COMSOL Multiphysics software in the frequency range of 1-15 GHz. The effective medium parameters i.e., effective permittivity, effective permeability and effective refractive index were calculated using Nicolson Ross weir method. Further, its Effective medium ratio (EMR), which is obtained 9.9 at 3 GHz operating resonance frequency, indicating the compactness of the structure.
Metamaterials are the sub-wavelength arrays of the composite structure made of metallic and/or dielectric materials. The metal-dielectric structure provides a significant enhancement in the field but has a high loss, low Q-Factor and poor spectral contrast in the visible and infrared frequencies. To overcome these problems, all-dielectric metamaterials structures are the better alternative which offers negligible losses due to their low absorption and hence they have narrow resonance peak and high spectral contrast. When all-dielectric metamaterial with specific geometry (asymmetric oscillators) interacts with the electromagnetic field in visible and infrared (IR) wavelength range, the interaction produces the Fano-Resonance. The Fano resonance depends on the shape and size of the metasurface structure and the refractive index of the surrounding. The Fano-resonance based on all-dielectric metamaterials can be used as a refractive index sensor for biomedical sensing and optical modulation in telecommunication. All-dielectric metamaterials based on Fano resonance can be utilized to have a high Figure-of-merit (FoM) refractive index sensor device. In this work, we are proposing a Fano resonance-based refractive index (RI) sensor which has a high FoM of the order of 2465.
In this paper, we proposed and theoretically simulated the tunable all-dielectric metasurface by varying the bisecting angular gap. The Fano-resonance position for the proposed silicon-on-silica structure shows the blue-shift with an increase in the angular gap. We have also observed the steep rise in the linewidth (FWHM) due to the increase in the angular gap. Such designs of the metasurfaces can provide a customized solution for various applications like modulator, filter, biochemical sensors.
In this work a novel design of an all-dielectric metamaterial perfect reflector has been proposed which exhibits 100% reflectance at a particular frequency and high reflectance in a broad range of wavelengths. This design is purely dielectric, hence, is free from resistive losses which are intrinsic to metallic thin film type reflectors. The design is compatible to on-chip fabrication techniques and can be realised by using well known methods such as optical lithography or electron beam lithography. The proposed structure can augment the performance of low loss cavity resonators, frequency selective filters, sensing, directive emission of radiation, etc.
In this paper, we have proposed and numerically investigated an all-dielectric metasurface consisting of a 2-dimensional periodic array of convex facing silicon asymmetric split arcs on the silica substrate. Due to split asymmetric arcs configuration, the structure exhibits Fano resonance at the wavelength of 967 nm. The maximum achieved quality factor (Q-Factor) and the spectral contrast ratio of the Fano resonance are 213.4 and 99.91%, respectively. The proposed metasurface can be used as a refractive index sensor as the resonance wavelength is linearly dependent on the refractive index of the surrounding. With the increase in the refractive index, the resonance wavelength shows the red-shift. We found that the wavelength shift per refractive index unit (RIU) is 250 nm/RIU and the figure of merit of this sensor is 50.
Experimental realization of a fiber Bragg grating-based compact, high-sensitive, and fully packaged single-axis accelerometer has been demonstrated. To verify experimentally observed results, simulation has been carried out for the performance comparison of packaged single-axis accelerometer with the cantilever of various materials. The experimental demonstrations have been conducted at unknown seismic vibrations of random frequencies as well as the vibrations of known frequencies. The experimental results for the reported seismic events (i.e., footprint and hammering) demonstrate that the developed fully packaged accelerometer possesses good response to the signals with random vibrations. The developed accelerometer holds a high sensitivity up to 88 pm/g in the broad bandwidth. Such a compact fully packaged accelerometer with improved sensitivity can be deployed at any civil engineering structures, such as highways, bridges, dams, tunnels, pipelines, and aeronautical platforms for broadband dynamic monitoring of the random vibrations ranging from 5 to 100 Hz.
In this work, a novel design of dielectric zero-index metamaterial (ZIM) filled photonic crystal defect waveguides have been proposed. The ZIM used here is basically a photonic crystal having Dirac cone at gamma point of the band structure. Existence of Dirac cone implies the linear dispersion in the vicinity of the Dirac point which is the main reason behind the zero-index behaviour. It has been shown in this article, that when such metamaterial is inserted inside a photonic crystal defect waveguide it reduces the effect of bending on transmission coefficient as compared to the conventional designs. The proposed design comprises of square arrays of Si rods in air, in which, the periodicity to wavelength ratio (a/λ) for ZIM and the surrounding photonic bandgap (PBG) structure are 0.541 and 0.35 respectively. Wavelength of operation is 1550 nm. Furthermore, as the ZIM is made up dielectric only, its free from ohmic losses.
We have designed and analysed a rib waveguide structure in recently reported Ga-Sb-S based highly nonlinear
chalcogenide glass for nonlinear applications. The proposed waveguide structure possesses a very high nonlinear
coefficient and can be used to generate broadband supercontinuum in mid-infrared domain. The reported design of the
chalcogenide waveguide offers two zero dispersion values at 1800 nm and 2900 nm. Such rib waveguide structure is
suitable to generate efficient supercontinuum generation ranging from 500 – 7400 μm. The reported waveguide can be
used for the realization of the compact on-chip supercontinuum sources which are highly applicable in optical imaging,
optical coherence tomography, food quality control, security and sensing.
All-dielectric nanoparticles have attained a lot of attention owing to the lesser loss and better quality than their metallic
counterparts. As a result, they perceive applications in the field of nanoantennas, photovoltaics and nanolasers. In the
dielectric nanoparticles, the electric and magnetic dipoles are created in dielectric nanoparticles when they interact with
the light of a particular frequency. Kerker’s type scattering is obtained where electric and magnetic dipoles interfere. In
our design, Silicon cylindrical nanoparticles having radius of 70 nm and length 120 nm have been considered. The
propagation of light is taken along the length of the cylinder. The scattering cross section has been obtained and plotted
with respect to the wavelength. At the peaks of scattering spectra, electric and magnetic dipoles are created at the
wavelengths of 510 nm and 600 nm, respectively. Both dipoles interfere at the wavelengths of 550 nm and 645 nm. At
these wavelengths, far field scattering pattern has been calculated. At the wavelength 645 nm, forward scattering takes
place because electric and magnetic dipoles are in phase at this wavelength. Further, directivity is enhanced by taking the
planar array of the nanoparticles. It has been observed that directivity increases by increasing the size of the array. Also,
there is an increase in the directivity by increasing the gap between the nanoparticles. This enhancement of directivity
can lead to the design of all dielectric cylindrical nanoantennas.
In this paper, a design of Plasmonic waveguides based optical AND gate has been proposed. Various designs of Photonic crystal based optical logic gates have already been envisioned and proposed during the past decade, in which, wavelength of operation is comparable to the geometrical parameters. On the contrary, the proposed structure consists of Plasmonic waveguides whose thickness is much smaller than the wavelength of operation. Plasmonics can pave way for the development of optical interconnects that are small enough to operate in nanoscale devices. Nowadays, Plasmonics is being implemented in a large number of areas, one of which is confinement of optical power in subwavelength devices. This may pave the way for large scale on-chip integration for the development of all optical circuits for optical computing systems. Moreover, the proposed design is simple and easy to fabricate using techniques like thin-film technology and lithography. This AND gate has been designed and analysed using the Finite Element Method (FEM) software. The proposed structure has been made by using silver material as a waveguide and silicon as the surrounding dielectric..
In this paper we present the design of a metamaterial perfect absorber (MPA) made up of an array of dielectric microcubes grown on a metallic substrate. The fundamental principle of operation of the proposed structure is Mie Resonance occurring in high permittivity particles in combination with the negative permittivity provided by the metallic substrate. The proposed structure is simpler than all other existing metamaterial perfect absorber structures. The geometrical parameters of the structure are between 1 μm and 10 μm, hence it is not supposed to pose any challenge during fabrication. Moreover, the structure has been designed for terahertz spectrum which is the most unexplored part of the spectrum.
In this paper, study of novel design of gold tip slotted square patch nanoantenna placed over silica substrate has been done. Designed antenna is optimised on basis of various geometrical parameters such as antenna length, thickness, gap between the antenna etc. using COMSOL Multiphysics a finite element method (FEM) based simulation software for the near field analysis. Both single and coupled tip slotted square patch antenna are analysed and the effect of slot on the antenna performance is also studied. The operational wavelength is in the near and mid infrared range of the electromagnetic (EM) spectrum as nanoantenna finds various applications in the field of near field microscopy, spectroscopy, infrared(IR) detection, waste energy and solar energy harvesting.
A photonic crystal fiber (PCF) structure in Ga–Sb–S-based chalcogenide glass has been designed for nonlinear applications. The propagation characteristics of the designed structure have been investigated by employing COMSOL multiphysics software based on a full-vectorial finite element method. The proposed PCF structure possesses a nonlinear coefficient as high as 14.92 W−1 m−1 with the effective mode area of 3.37 μm2 at the operating wavelength of 1.55 μm. The proposed structure exhibits a flat and low dispersion value between spectral spanning 2.4 and 2.7 μm with a maximum dispersion variation of 20 ps/nm km. To the best of our knowledge, the PCF design is investigated for first time in Ga–Sb–S-based chalcogenide glass. The structure possesses a zero dispersion wavelength value at 2.6 μm. The structure is a promising candidate for nonlinear applications, such as midinfrared supercontinuum generation, slow-light generation, and midinfrared fiber lasers.
A design of split-nanotube-based negative index metamaterial for the infrared spectrum has been proposed. The proposed design and its operation are similar to that of a split-ring resonator (SRR) without inheriting the fabrication difficulties associated with conventional SRR. A negative refractive index has been achieved using a split-nanotube in combination with a periodic array of metallic wires between 1.5 and 3.3 μm.
We theoretically demonstrate ultradirectional, azimuthally symmetric forward scattering by dielectric cylindrical nanoantennas for futuristic nanophotonic applications in visible and near-infrared regions. Electric and magnetic dipoles have been optically induced in the nanocylinders at the resonant wavelengths. The cylindrical dielectric nanoparticles exhibit complete suppression of backward scattering and improved forward scattering at first generalized Kerker’s condition. The influence of gap between nanocylinder elements on the scattering pattern of the homodimers has been demonstrated. Further, for highly directive applications, a linear chain of ultradirectional cylindrical nanoantenna array has been proposed.
In the present paper, we have carried out analysis of asymmetric light propagation in a chirped photonic crystal (PhC) waveguide. The designed structures have hexagonal arrangement and square arrangement of Silicon (Si) rods in air substrate. Dimensions of the defect rods is tailored, so that the proposed design structure work as an optical isolator. The transmission analysis of the structure reveals that it can act as an optical diode. We have plotted the extinction ratio and transmission analysis graphs for the structure and it has been observed that maximum output is obtained for telecom wavelength of 1.55μm.
A tunable cylindrical all dielectric optical nanoantenna has been proposed. A silicon nanocylinder of radius 60 nm and
height 150 nm has been considered. The azimuthally symmetric, complete forward scattering at first Kerker’s condition
and backward scattering with minimum forward scattering at second generalized Kerker’s condition in near infra-red
region has been observed for the proposed design which makes silicon nanocylinder a promising candidate for optical
nanoantenna applications. The effect of the dimensions of the dielectric nanocylinder on the scattering properties of the
cylindrical nanoantenna has been analyzed using finite element method. We have analyzed that the variation in diameter
of nanocylinder has great influence on the strength of interference of electric and magnetic dipolar resonances. Further,
we have observed tuning ability of the cylindrical nanoantenna with respect to the variation in its radius.
In this paper we discuss the role of evanescent waves in nanophotonic devices, especially in metamaterials. We discuss how metamaterial cladding increases the power confinement in waveguides by increasing the momentum of evanescent waves. The momentum of evanescent waves is controlled in such a fashion that condition of total internal reflection is not disturbed. This becomes possible by making the cladding anisotropic. Anisotropic cladding gives the facility to control the parallel and perpendicular components of wave vector individually. We analyze the efficiency of this technique in case of waveguides. We have also discussed the advantages of collecting evanescent waves for imaging sub wavelength objects.
In this paper, electric and magnetic resonances induced in the ellipsoidal dielectric nanoparticles in the optical range have been analyzed. Circular displacement currents excited inside the elliptical nano-particles by the incident light result in magnetic dipolar resonance in the dielectric nanoparticles. Kerker’s type scattering is observed due to the mutual interference of electric and magnetic resonances. The effect on the resonance conditions with the variation in the relative permittivity from Er= 5 to Er= 20 of the ellipsoidal nanoparticle has been observed. It has been analyzed that peaks of electric and magnetic resonances come closer by decreasing the electric permittivity of the nanoparticle, which leads to the increase in the directionality in the forward direction, as verified using Generalized Kerker’s condition. Further, far field scattering patterns have been obtained using the finite element method. Here, the electric and magnetic resonances have been optically induced up to quadrupolar modes. There is enhancement of the directionality in the forward direction when electric and magnetic resonances are in phase. Further, the effect of size of the linear array of ellipsoidal nanoparticles on the directionality has been analyzed. It has been observed that there is increase in the directivity by increasing the chain of the nanoparticles. Thus, the ellipsoidal nanoparticles can lead to the design of low loss and highly directional optical nanoantennas.
In this paper, enhanced image resolution by modification in the two dimensional (2-D) photonic crystal structures has
been proposed. The equal frequency contour (EFC) analysis have been done using plane wave expansion method which
shows that the structure exhibits an effective isotropic refractive index, neff = -1 at a normalized frequency of ω =
0.2908(2πc/a) for TM polarization, located near the second band. At ω = 0.2908(2πc/a) for TM polarization, the
considered PhC structure behaves as a superlens, as analyzed using the finite difference time domain (FDTD) method.
The image resolution and stability of the photonic crystal slab lens has been enhanced by creating disorder in the top and
bottom layer of the PhC structure. The intensity field distributions of the optimized structure exhibit the enhanced image
quality with full width at half maximum (FWHM) of 0.311 λ. The proposed structure can also be used to sense the
different type of blood constituents.
In this paper, we have proposed the design of all-optical AND logic gate using the combination of universal
NAND gates. The structure consists of hexagonal arrangement of air holes in silicon. The proposed structure has
been designed using the finite difference time domain (FDTD) method. The optimized NAND gates have been
arranged in a combination such that the combined structure behaves as an all-optical AND logic gate. The
proposed structure exhibits a response period of 6.48ps and bit rate of 0.154 Tb/sec.
Propagation characteristics of a cladding doped defect-core large mode area W-type photonic crystal fiber have been
investigated by using finite element method. In the proposed structure the central air hole has been removed to form the
defect core and the second layer of cladding rings around the central core have been selectively doped with different
concentration of fluorine to tune the refractive index of the doped silica rods. The bend loss, dispersion, effect of bending
on dispersion, and nonlinear coefficient of the proposed photonic crystal fiber design has been numerically investigated.
The proposed W-type photonic crystal fiber has low bend loss, low dispersion, large-mode-area with low value of
nonlinear coefficient at wavelength of 1.55μm. The structure can be utilized for telecommunication applications, for
applications in high power fiber lasers, amplifiers and sensors.
We propose a design for a polarization beam splitter based on the phenomenon of a photonic crystal directional coupler. The design consists of a honeycomb lattice arrangement of air holes of different radii in a silicon-on-insulator substrate exhibiting a complete photonic bandgap. The results obtained by the finite-difference time domain method show that the extinction ratio for transverse electric (TE) and transverse magnetic (TM) polarizations is 24.56 and 28.29 dB, respectively, at a wavelength of 1.55 μm. The degree of polarization for TE polarization is 99.29% and for TM polarization is 99.70%. Hence, the proposed design can be efficiently used as a polarization splitter for on-chip integrated devices.
The terahertz and mid-infrared region of the electromagnetic spectrum is relatively new area of interest and incorporates a wide range of applications from image sensing to spectroscopy and many more yet to be discovered. In the area of metamaterials many new designs have been discovered, but “chevrons” shaped split ring resonators (ch-SRRs) in the mid-infrared region has not been studied to the best of our knowledge. This paper presents the analysis and simulation of ch-SRRs in the mid infrared region. Tunability of SRRs is important for various industrial and scientific applications and hence this paper analyzes the tunability of the ch-SRRs by variation of angle. The device is simulated in two configurations i.e., one with two chevrons shaped SRRs on the same plane of the dielectric substrate and the other with each of the two chevron shaped SRRs on the opposite plane of the substrate. Gold SRRs is used, since we are working in the terahertz region Lorentz-Drude model is employed to incorporate the losses. The ch-SRRs have been embedded upon the silicon substrate. The models are designed and simulated in COMSOL and result is shown in MATLAB. The results obtained for reflectance are of particular interest. The effective medium parameters viz. Impendence, permittivity, permeability and refractive index obtained for the split ring resonator are also evaluated. This design shows sharp results for reflectance which can be used in sensors application.
Mie resonance in square arrays of dielectric rods has been reported. Arrays in square lattice of dielectric rods with very high permittivity in air have been considered. Light of transverse electric mode has been launched on the square array of cylindrical dielectric rods. Mie resonance of first two orders has been observed in the dielectric rods, due to which electric and magnetic dipoles are generated in the rods. Thus, electric resonance and magnetic resonance at different frequencies has been observed with material of high value of permittivity.
Cone shaped resonators have been proposed to create a near perfect metamaterial reflector in the visible range (640nm-680nm). Resonators are made up of high permittivity dielectric (Si). In the considered wavelength range reflectance is above 90% with maximum value of 99.5% at 660nm. It is Mie-Resonance based structure showing magnetic and electric resonance at different wavelengths.
Recently, photonic crystal fibers have attracted significant attention for their applications in optical fiber communication systems. In some polarization sensitive applications photonic crystal fibers with single-mode and single-polarization are desirable. In this paper, a rectangular-core single-mode single-polarization large-mode-area photonic crystal fiber structure has been designed based on higher order mode filtering. The single-polarization is obtained with asymmetric design and introducing different loss for x-polarization and y-polarization of fundamental mode. Single-polarization single-mode operation of a highly bi-refringent photonic crystal fiber is investigated in detail by using a full-vector finite-element- method with anisotropic perfectly-matched-layer. At optimized parameters, the confinement loss and effective-mode-area is obtained as 0.9 dB/m and 927 μm2 for x-polarization as well as 12.53 dB/m and 921 μm2 for y-polarization of fundamental mode respectively at 1.55 μm. Therefore, 1.6 m length of fiber will be sufficient to get x-polarized fundamental mode with effective-mode-area as large as 927 μm2.
In this paper, we have proposed a design for slow light effect in pinch photonic crystal waveguide. The design consists of two dimensional triangular arrangements of air holes in silicon on insulator substrate. From the calculations it has been found out that for the proposed structure the group index is high and group velocity dispersion is low. The confinement of light in the pinch waveguide with slow light effect can be a strong candidate for sensor applications.
A rectangular core photonic crystal fiber design in As2Se3 chalcogenide glass has been reported for mid-infrared supercontinuum generation. The structural parameters have been tailored for all normal dispersion profile. The proposed structure possesses nonlinearity (Υ) as large as 20956 W-1 km-1 at 2800 nm wavelength with very low and flat dispersion of -2.38 ps/(nm×km). We have generated supercontinuum spectra spanning 1480 – 9990 nm using only 4 mm length of proposed photonic crystal fiber pumped with femtosecond optical pulses of peak power of 500 W at 2800 nm.
In this paper, we have calculated the highly efficient generation of the slow light based on the Stimulated Brillouin scattering (SBS) in a small core As2Se3 chalcogenide PCF. A Brillouin gain coefficient, gB. of 9.05 10-9 m.W-1 is found around the acoustic frequency of 8.08 GHz in small core diameter of 1.69 μm with 1.5 μm2 effective mode area at 1550 nm. A Brillouin gain of 77.3 dB was achieved with only 10 mW pump power in a 10-m fiber length, which leads to the optical time delay of 94 ns. In terms of the proposed figure of merit, it shows 2.77 dB/mW/m which is about 110 times more efficient than conventional single-mode fibers. These fibers are expected to have potential applications in realization of compact slow light devices.
We have proposed a design for slow light with ultraflat dispersion in a slotted photonic crystal waveguide consisting of a hexagonal arrangement of elliptical air holes on a silicon-on-insulator substrate. The proposed structure has low group velocity and low group velocity dispersion with a wide normalized bandwidth range of 0.0089. The proposed structure can be used as an optical buffer for the storage of a large amount of data due to the large value of the normalized delay bandwidth product equal to 0.634. An optimized structure for a slotted photonic crystal has been analyzed for its applications as both a time and wavelength division demultiplexer. Furthermore, the time delay between two adjacent wavelengths (1550 and 1555 nm) is more than that reported earlier.
Stimulated Brillouin scattering (SBS) performances of small core tellurite photonic crystal fibers (PCF) are rigorously studied. We propose a design of tellurite PCF that is used for slow-light-based applications. We developed a two-dimensional finite element mode solver to numerically study the acoustic and optical properties of complex refractive index profiles including tellurite PCF. Our results include the calculation of Brillouin gain spectrum, Brillouin gain coefficient (gB) and Brillouin frequency shift by taking into account the contribution of the higher-order acoustic modes. Several simulations were run by varying the air-filling ratio of various PCF structures to enhance the SBS. The real scanning electron microscope image of a small core of highly nonlinear tellurite fiber is considered. Optimized results show a frequency shift of 8.43 GHz and a Brillouin gain of 9.48×10−11 m/W with a time delay between 21 and 140 ns. Such fibers have drawn much interest because of their capacity for increasing and tailoring the SBS gain.
In this work we propose and study a highly sensitive quantum dot (QD)-metal film plasmonic
composite. The system comprises of indium arsenide (InAs) QDs on silver film. The intensity
is traced by scanning the absorption spectra for the system. We found that the behaviour of
the plasmonic composite changes by varying the thickness of metal film. It is observed that
the sensitivity of the composite varies with the thickness of metallic film and the quantum
size effects dominate at sub-nanometer gap. The proposed system shows promising
applications in lasing, sensing and spectroscopy.
A new design of the As2Se3 microfiber has been presented. With the optimized geometric parameters: pitch Λ= 0.8 μm
and five different air filling ratios varying from 0.4 to 0.95, the structure exhibits an all normal dispersion with a flat top
equal to -2.3 [ps/(nm.km)], a confinement loss less than 10-2 dB/km, and a large nonlinear coefficient equal to 7250 (w.
km)-1. Using the generalized nonlinear Schrödinger equation, we generate a very broadband supercontinuum (SC) in the
mid-infrared region. By pumping the fiber at λp=5.24 μm with a femtosecond laser having 50 fs as a width with a
relatively low energy of E=80 pJ, we generate a large spectrum extending from 2 μm to 10 μm in only 2 mm fiber
length. The generated SC demonstrates perfect coherence property over the entire bandwidth. SC generation extended
into the mid-infrared (IR) spectral region have potential usefulness in a variety of applications requiring a broad mid-IR
spectrum such as fiber sensing, IR spectroscopy, fiber laser, optical tomography coherence.
A single mode microstructured polymer optical fiber has been designed and analysed based on finite element method
(FEM). The design parameters of proposed microstructured polymer optical fiber structure have been optimized to obtain
single mode operation along with mode area of 895 μm2. The differential loss between fundamental and higher order
modes of structure have been obtained very large (~103) with negligible loss of fundamental mode. The proposed
structure is effectively single mode at 632.8 nm wavelength after the short distance 1.65 m with very low loss of guiding
mode. The proposed structure is applicable for high power delivery devices.
An equiangular spiral (ES) photonic crystal fiber (PCF) design in tellurite glass has been presented. The structure
parameters have been tailored for zero dispersion wavelength (ZDW) at λZDW=1570 nm. The fiber structure has high
nonlinearity (γ = 2000 w-1 Km-1) at 1550 nm wavelength with very low and flat dispersion -0.152 [ps/(nm×km)]. We have generated supercontinuum using only 2 mm length of tellurite ES PCF with low input pulse energy of 200 pJ by
pumping at 1550 nm. The proposed fiber may be a suitable candidate for nonlinear applications.
Photonic crystal based nano -displacement sensor for horizontal as well as vertical displacement has been proposed. The
design is highly sensitive in the displacement region 40nm–120nm with sensitivity 0.00461nm-1 for horizontal
displacement of the moving PhC waveguide. For vertical displacement of the moving PhC waveguide the design is
highly sensitive in the region 150nm-200nm with sensitivity 0.00684nm-1 for zero horizontal displacement, 130nm-
200nm with sensitivity 0.00523 nm-1for 10nm horizontal displacement, 130nm-200nm with sensitivity 0.00418 nm-1 for 20nm horizontal displacement, 130nm-200nm with sensitivity 0.00461 nm-1for 30nm horizontal displacement,100nm-130nm with sensitivity 0.00466 nm-1for 40nm horizontal displacement. It has been concluded that the proposed design behaves as a Nano-displacement sensor for horizontal displacement of the moving PhC waveguide up to the region of displacement of magnitude of 400nm and for vertical displacement of the moving PhC waveguide up to the region of
displacement of magnitude of 300nm.The proposed design can behave as a nano-Displacement sensor for both horizontal
as well as vertical displacement.
A novel design of single polarization single mode (SPSM) photonic nanowire is proposed. Using a cladding structure
with circular air holes, a new design of a photonic nanowire with ultra-wideband range of 740 nm for SPSM operation is
obtained. The numerical results show that the SPSM-nanowire is low-loss within the wavelengths ranging from 1.17 μm
to 1.91 μm, the confinement loss of the slow-axis mode is less than 0.15 dB/km and the fast-axis mode is unguided. This
fiber has greater advantages in polarization sensitive applications, such as fiber optic gyroscopes, fiber optic current
sensors, high-power fiber lasers, and coherent optical communications.
The proposed paper calls attention towards the unobserved mathematical and conceptual inadequacies persisting in the wave-particle duality and matter wave’s concepts, given by Louis de Broglie. Matter wave’s frequency and phase velocity expressions, shown to be inappropriate, are the consequences of these inadequate concepts. The rectifications in these concepts are presented through the corrected implementation of analogy between light waves and matter waves and thus modified frequency and phase velocity expressions are introduced. The proposed expressions are free from all the inadequacies and negations, contrary to that confronted by de Broglie’s proposed expressions. Mathematical proofs for the proposed modified frequency and phase velocity expression are also presented. A novel General Quantum Mechanical Wave Equation is proposed involving the modified phase velocity expression, which itself can precisely derive out Schrodinger’s and Dirac’s Equation.
Photonic crystals (PhCs) have emerged as one of the most significant topics in the field of optical communication since their first introduction by Yablonvitch 1 and John 2. Recently, interest has been grown in the design and development of optical logic gates based on different schemes 3-10. In this paper, we report the design of optical logic AND gate based on two structures, one of which is a hexagonal lattice with silicon (Si) rods in air (SRA) and another is the hexagonal lattice arrangement of air holes in silicon (AHS) with air waveguides. Both the gate structures are based on Y shaped PhC waveguides and analyzed by plane wave expansion (PWE) method. The simulation results show that the proposed structures operates as an AND gates and has a bit rate of 2.016Tbit/s for SRA and 1.785Tbit/s for AHS structure. By appropriately choosing the size and the interaction length of the central rod in SRA and size of central hole in AHS, the optimal performance of the proposed AND logic gates has been achieved.
A large-mode-area (LMA) single-mode (SM) photonic crystal fiber (PCF) structure for applications in high power fiber lasers, amplifiers and sensors is proposed. In the proposed structure the center air hole has been removed to form the core and the six elliptical air holes of inner ring around the center core have been selectively filled with high refractive index material. Effects of design parameters on SM operation and mode area are numerically investigated by using the full vectorial finite-element method. Structure offers large-mode-area exceeding 835 μm2 at 1.064 μm wavelength. A PCF with such a large-mode-area would significantly reduce the nonlinear effects and would be useful for high power applications.
We present a multi-trench channel waveguide design that supports a single-guided mode with large-mode area. Geometrically shaped waveguide with suitable design parameters ensure effective single-mode operation by introducing high leakage loss to higher-order modes while a nominal loss to the fundamental mode. A waveguide of ~ 2.2 mm length is able to ensure single-mode operation with the core area of 100 μm2. Such a large confinement area for mode propagation can effectively suppress nonlinear optical effects. The proposed channel waveguide structure is expected to find applications in high power devices and components such as high power waveguide lasers, amplifiers and sensors.
In this paper we investigate potential of plasmonic nano switch as a result of Fano-resonance
observed in periodically arrayed silver (Ag) nanoparticles embedded over silicon (Si) on
insulator (SOI) substrate, by using 3D finite difference time domain (FDTD) method.
Structural parameters of the embedded silver nanoparticles were optimized giving rise to
plasmon modes in the device. We find that as the device is scanned for a range of wavelength
varying from visible to near infra-red, the transmission spectra exhibits Fano-line shape
asymmetry for input wavelength regime near 1.3 - 1.55micron, whereas normal resonating
peak is observed in the visible region. The optical properties of the switch reveal,
enhancement in transmission due to strong plasmonic Fano resonance between the
background and resonant processes. Sharp Fano-resonance, specific to interacting quantum
systems, is exhibited by the proposed embedded hybrid design of metal nanorods into Si,
which meets the condition required for high contrast switches and hence can be exploited as
per anticipated results. Fano resonance in this nanorod-substrate system can also be used for
designing nanoantennae, lasers, sensors, SERS etc.
A hybrid metal photonic crystal based nanostructured cavity and waveguide for the sub-wavelength confinement of light is proposed and it is shown that a bottom reflector is vital for the vertical emission from a silicon (Si) photonic crystal (PC) nanocavity. A photonic crystal slab of Si (εd=11.56 or nd=3.4) with air holes and metal as an underlying substrate is chosen and three dimensional (3D) photonic bandgap for structure is calculated with plane wave expansion (PWE) method. Using finite difference time domain (FDTD) method, the transmission of a cavity mode as a function of Photonic crystal slab thickness is calculated and it is observed that the transmission increases with the increase in slab thickness at wavelength, λ = 1.55μm. Also, transverse electric field profiles (Ey) of the cavity mode has been shown and quality factor are calculated for the cavity and possible application in the area of PC light based emitters such as plasmonic lasers and single photon source is assessed.
In this paper, a design of Planar Metamaterial Optical Antenna based on split ring resonance (SRR) structure is
reported. The design exploits the special property of the metals and metamaterials. Metal acts as strongly
coupled Plasmon in nano-scale range when operated at optical frequency. Planar metamaterial exhibits its
optical properties from the structure rather than the composition. The structure of planar metamaterial antenna is
tailored in such a way that it will yield an antenna of high directivity and enhanced intensity response in the
optical frequency regime.
We theoretically investigate compact plasmonic coupler based on metal nanopillar over silicon on insulator substrate
demonstrating routing of light at nanoscale. Proposed geometry demonstrates strong mode confinement, allows sharp
bends with low loss and easy integration on chip circuitry. The coupler is optimized for visible regime and can be tuned
for specific wavelengths. Plasmonic transverse magnetic (TM) modes are observed and examined using finite difference
time domain (FDTD) computations. Coupling length (Lc) and gap width (Wc) for the nanopillar assisted four-port
plasmonic coupling structure is optimized to give enhanced efficiency. The structure renders subwavelength light
manipulation overcoming conventional photonics with applications in plasmonic circuitry for nanoscale guidance of
light in data transmission, integrated chip design etc.
The effects of the slow-down factor on third-order nonlinear effects in silicon-on-insulator photonic crystal channel waveguides were investigated. In the slow light regime, with a group index equal to 99, these nonlinear effects are enhanced but the enhancement produced depends on the input peak power level. Simulations indicate the possibility of soliton-like propagation of 1 ps pulses at an input peak power level of 50 mW inside such a photonic crystal waveguide. The increase in the induced phase shift produced by lower group velocities can be used to decrease the size and power requirements needed to operate devices such as optical switches, logic gates, and wavelength translators.
In this paper, soliton pulse generation and collision in chalcogenide As2Se3 glass Photonic Crystal Fiber (PCF) is
numerically studied using our own algorithm developed for
Fourth-Order Runge-Kutta in the Interaction Picture
(RK4IP) method. The numerically obtained value of soliton collision length is found to be in good agreement with the
theoretical value obtained by the inverse scattering transform, thus providing a verification of the accuracy of the method
in solving Generalized Nonlinear Schrödinger Equation (GNLSE). We also calculate the value of wavelength for least
distortion for soliton optical pulses.
In this paper, we report design and development of optical sensor for the determination of adulteration in petrol using
optical time-domain reflectometer (OTDR). OTDR is generally used to find out fault in optical fibers but we effectively
use this technique for the determination of the percentage of adulteration in petrol. This OTDR method enables detection
of adulteration in petrol very accurately. The OTDR measurement method reported in this paper is easy to carry out and
also a cost effective tool for the determination of adulteration in petrol.
We examine the propagation of plasmonic TM (Transverse Modes) modes generated in the designed periodic array of
silver (Ag) embedded on silicon (Si) substrate. The properties of surface plasmons are tailored by altering the size of Ag
nanorods and its periodicity. Conventional waveguides cannot guide electromagnetic energy below the diffraction limit
of light, which can be overcome by texturing the metal or dielectric surface. In this hybrid design we have textured the
interface by placing metallic, Ag nanorods on Si substrate placed over bilayer system of glasses. This provides the
missing momentum required, since SPP modes always lay beyond the light line and has shown strong confinement of
light. Ag nanorods are structured at nano dimensions to control and manipulate surface plasmon polariton (SPP) propagation and thus open new possibilities in light matter interaction.
Dispersion and resonance properties of double nanorod structure, ring structure, H structure and chair type structure is
demonstrated. With some structural modification, the properties of the structure changes from isotropic to uni-axial
anisotropic and further to chiral left-handed material. The Demonstration of near-field transmission spectrum reveals the
production of the local-field enhancement up to 102 for the green light. Negative real values of both permeability (μ) and
permittivity (ε) for visible light are obtained by applying coupled dipole approximation. The structure modification
exhibits some unique dispersion and resonant properties that may govern imaging applications.
The effects of different slow-down factors on two photon absorption and free carrier absorption in silicon-on-insulator
(SOI) photonic crystal (PhC) channel waveguides are reported in this paper. It is found that, in the slow light regime,
these nonlinear effects are enhanced, but that the enhancement produced depends on the input peak power level.
Simulations indicate the possibility of soliton-like propagation of 111 fs pulses at 1.55 μm inside such a photonic crystal
waveguide.
A plasmonic cavity incorporating surface plasmon polariton(SPP) mode is proposed to be used as infiltrated sensor
employing sub-wavelength confinement of light. Truly Plasmonic TM mode is obtained and the mode profile of the
Plasmonic Photonic Crystal Cavity (PPCC) structure is shown using three dimensional Finite Difference Time Domain
Method (3D-FDTD) method. The cavity length of the structure is optimized to obtain single mode localization of
resonating wavelength and the change in the cut-off wavelength is observed by varying refractive indices of the content
of air holes. A transverse magnetic (TM) Plasmonic bandgap of the structure is shown and hence, the transmission
spectra, Quality factor are calculated.
Plasmon like excitation is observed at the interface between
one-dimensional periodic array of air holes in
silicon (Si) with ferroelectric polyvinylidene fluoride (PVDF) as a substrate to obtain subwavelength
confinement of surface Plasmon modes at terahertz (THz) frequencies. A truly Plasmonic TM mode is obtained
confined at the interface of PVDF layer and the 1D perforated dielectric slab and the mode field distribution of
the structure is demonstrated using three dimensional (3D) Finite Difference Time domain Method (FDTD)
method. It is shown that PVDF are promising materials for strongly confined THz wave propagation in Surface
Plasmon photonic crystal. The transmission, confinement and hence the propagation length of the plasmonpolariton
like terahertz surface modes sustained by the structure are studied using Finite difference time domain
(FDTD) method. Further, the propagation characteristics of surface Plasmon polariton (SPP) which can be
controlled by the structure geometry is discussed.
One-dimensional (1D) surface plasmonic (SP) nanostructured cavity for the sub-wavelength confinement of light is
proposed. Since, the significant spatial confinement of the plasmonic structure is needed for the miniaturization of the
device, thin silver metal sheet is used to get plasmonic mode of the cavity. 1D plasmonic photonic crystal structure is
designed by placing a silver substrate film(εm) below the photonic crystal waveguide of one dimensional array of air
holes in Si (εd=11.56 or nd=3.4) slab of finite thickness. TM mode with vertical electric field is investigated and it is
observed that the mode remains dominant in the structure. Further, surface plasmonic nano cavity defect mode is studied
by changing the cavity length which can be tuned for different wavelengths by changing the geometry of the structure.
A left-handed plasmonic optical nanoantenna is presented to demonstrate blue light generation with the
incident red light through second harmonic generation. Negative real values of permeability and permittivity with
extremely low imaginary values for visible light is obtained by applying coupled dipole approximation. Near-field and
far-field resonance spectrums reveal high directionality for the designed nano-antenna.
Infiltrated liquid sensors based on a 2D photonic crystal waveguide were devised. This waveguide is designed by taking into account lowering of the radius of the central air holes in a single row and the optical resonance shifts due to refractive index change of these holes by selectively filling with different liquids. The transmission spectrum of the infiltrated liquid sensor was obtained with the use of a finite difference time domain method. At the working wavelength of 1550 nm, the waveguide mode gap edge shifts with sensitivity of 200 nm per refractive index unit. The mode gap shifts are consistent with dispersion diagrams.
A new design of superior gain assisted double-negative plasmonic nanoantenna to demonstrate nonlinear
effects in UV/visible region. Demonstration of near-field transmission spectrum reveals the production of the local-field
enhancement up to 102 for half wavelength generation with the incident light wavelength in double nanorod-antenna
(DNRA) system and UV/ white light super-continuum generation for the nanoantenna array (NA) system. Negative real
values of both permeability (μ) and permittivity (ε) with extremely low imaginary values for visible light is obtained by
applying coupled dipole approximation. Near-field and far-field resonance spectrums reveal light amplification and high
directionality for the designed nano-antenna.
In this paper all the key parameters i.e. V-Number, effective refractive index of the cladding, radius of the core,
numerical aperture, mode field diameter (MFD) and mode field area have been obtained by Far-Field intensity
pattern of endlessly single mode Photonic Crystal Fiber (ESM-PCF). The transmission characteristics of PCF are also
analyzed and simulated using Improved Effective Index Method (IEIM). Results obtained from Far-field technique
and IEIM are compared and found in good agreement. Hence, IEIM is experimentally supported by the far field
technique.
A low-loss low-velocity photonic crystal (PhC) waveguide having rectangular air holes in-filled with a liquid
crystal in Si core is proposed. The possible propagation losses due to inefficient coupling are also investigated for
proposed structure. It is found that high transmission is obtained for a broad bandwidth from the output of the finally
designed heterogeneous waveguide consisting of a slow liquid crystal infiltrated PhC waveguide surrounded by fast PhC
waveguides on both sides.
A new simplified structure of highly birefringent chalcogenide As2Se3 glass Photonic Crystal Fiber (PCF) with
low confinement loss is designed and analyzed by using fully-vectorial finite element method. The effective indices,
confinement losses, birefringence and chromatic dispersion of fundamental polarized mode are calculated in the proposed
PCF. It is also shown that As2Se3 glass PCF provides lower chromatic dispersion and less confinement loss compared to
silica PCF of the same structure and hence such chalcogenide As2Se3 glass PCF have high potential to be used in dispersion
compensating and birefringence application in optical communication systems.
The development of theoretical and experimental method for the characterization of Polarization Maintaining Photonic
Crystal Fiber (PM PCF) from far filed intensity measurements has been reported. To maintain the polarization in PCF
different air hole diameter along orthogonal axes adjacent to the core region has been introduced. This helps in creating
an effective index difference between the two orthogonal polarization modes. It is shown that air hole spacing (Λ), air
hole diameter (d) and effective cladding index differences of PM-PCF can also be obtained from its far field
measurements.
In this paper, we propose silicon-on-insulator (SOI) based Photonic Crystal waveguide with hexagonal
arrangement of elliptical air holes embedded in silicon material for slow light transmission. Delay bandwidth product
which indicates the buffering capacity is evaluated to be record high 87.41 and large bandwidth (≈ 4.4THz) below silica
light line. Within this bandwidth, group velocity dispersion is evaluated on the order of 100-102 ps2/km. Thus in the
proposed structure, light is confined horizontally by photonic band gap, vertically by total internal reflection and
longitudinally by low dispersion and low group velocity while propagating through the waveguide.
In the proposed paper, we present the guiding properties of chalcogenide Photonic Crystal Fiber (PCF) with
square and hexagonal arrangement of air holes in the cladding. The dispersion curves of chalcogenide PCF with different
hole-to-hole spacing and air hole diameter have been calculated. Application specific design of dispersion properties like
zero dispersion at any wavelength and negative dispersion will be reported for chalcogenide PCF. A comparison between
hexagonal and square lattice of chalcogenide PCF has also been performed.
An artificial engineered structure of nano-inclusion made of metallic nano-rods embedded in a dielectric
(ε=12.96) matrix with hexagonal arrangement is proposed. New improved designed structure exhibits Negative
Refraction (NR) in visible region by using surface plasmon wave in metallo-dielectric photonic crystal operating in a
dispersion regime with anti-parallel refracted wave vector and Poynting vector. Finite Difference Time Domain (FDTD)
simulations are carried out to study the reflection and transmission properties and obtained Far-field pattern. Designed
structure gives NR with high transmission and act as a filter with a quality factor ≈ 102 with strong application potential
in nano-optics and nano-technology.
In this paper, superprism phenomena based on phase velocity has been studied. PCs composed of air holes of
different shapes in a triangular lattice with constant filling fraction have been taken under study. The
observation of superprism behavior has been made using angle sensitive and wavelength sensitive propagation
of light. It has been found that the PC with hexagonal rod geometry yields the best behavior of the superprism in
the case of angle sensitive propagation. For wavelength sensitive propagation PCs with hexagonal and circular
air holes provide almost the same angular separation. Therefore we can conclude that the PC with the air-rod geometry of hexagon is the most suitable candidate for optical devices based on superprism phenomena.
A design of polarization beam splitter based on negative refraction in photonic crystal is proposed. The proposed structure is formed by a hexagonal lattice of embedded air holes in silicon materials and is based on 2-D photonic band structure and equi-frequency contour calculations where negative refraction is considered to be function of incident angle and thickness of slab. The designed structure exhibits oppositely signed (negative and positive) refraction for TE and TM polarization at telecom wavelength windows. The wavelength response of the designed PBS is obtained for both polarizations.
Dual Band Wavelength Demultiplexer (DBWD) is designed to separate two telecommunication wavelengths, 1.31μm
and 1.55 μm utilizing photonic crystals (PhC) in Silicon on Insulator (SOI). The waveguides formed in such PhC
structures confine light horizontally by a photonic bandgap and vertically by total internal reflection. Plane Wave
Expansion (PWE) method and Finite Difference Time Domain method are used to design and analyze the DBWD in Y
type PhC. Numerical analysis indicates that the separation of two wavelengths with enhanced extinction ratio,
transmittance and quality factor can be achieved, which confirms the superior performance of the proposed design of
DBWD
We explore the application of photonic band gaps (PBGs) in photonic crystal structures to propose the design of an ultracompact PBG polarizer. The existence of complete PBGs in certain photonic crystal structures and the variation introduced in the PBGs by the creation of defects has been utilized to design a PBG polarizer at 1.55 µm with a degree of polarization equal to 1 leading to the formation of a super polarizer.
In this paper, we report the highly birefringent elliptical core photonic crystal fibers (EC-PCF). The scalar and vectorial effective index methods are used to obtain the average refractive index of 2D triangular photonic crystal cladding. The first order perturbation technique is used to obtain the birefringence properties of EC-PCF. Birefringence of the EC-PCF obtained, is in the order of 10- 2, which is 10 times higher than that reported for conventional elliptical core fiber. It is shown narrowing the space between the air holes and enlarging the air-hole size in the cladding of PCF can achieve high birefringence. It is observed that for every design of PCF, an optimum hole-pitch exhibits for which EC-PCF shows high birefringence. Further, the effect of core area on birefringence is also studied and it has been revealed that high birefringence can be obtained for smaller core area of EC-PCF. Both Scalar effective index and Vector effective index method with the perturbation approach are applied to compare the high birefringence of EC-PCF.
Certain select structures in photonic crystals (PhCs) exhibit complete photonic band gap i.e. a frequency region where the photonic band gaps for both polarizations (i.e. transverse electric and transverse magnetic modes) exist and overlap. One of the most fundamental applications of the photonic band gap structures is the design of photonic crystal waveguides, which can be made by inserting linear defects in the photonic crystal structures. By setting closely two parallel 2D PhC waveguides, a directional waveguide coupler can be designed, which can be used to design a polarization splitter. In this paper we design a polarization splitter in a photonic crystal structure composed of two dimensional honeycomb pattern of dielectric rods in air. This photonic crystal structure exhibits a complete photonic band gap that extends from λ = 1.49 μm to λ = 1.61 μm, where lambda is the wavelength in free space, providing a large bandwidth of 120 nm.
A polarization splitter can be made by designing a polarization selective coupler. The coupling lengths at various wavelengths for both polarizations have been calculated using the Finite Difference Time Domain method. It has been shown that the coupling length, for TE polarization is much smaller as compared to that for the TM polarization. This principle is used to design a polarization splitter of length 32 μm at λ = 1.55 μm. Further, the spectral response of the extinction ratios for both polarizations in the two waveguides at propagation distance of 32 μm has been studied.
Dispersion compensating discrete Raman amplifier are known to open up new wavelength bands. However there is also the issue of wastage of Raman pump power. The length of dispersion compensating discrete Raman amplifier is decided to minimize the dispersion. Hence significant pump power is wasted. In this paper, a novel design of dispersion compensating Raman/ Two stage EDFA hybrid is reported which recycles the residual pump power from the dispersion compensating Raman and feeds this pump to the second stage of two stage EDFA. The first stage is remotely pumped from another laser source. Using this configuration, we have achieved an extremely large gain bandwidth of 117.5nm from 1582.5-1700nm with a 3dB ripple, has been achieved This amplifier topology while using minimum no of pump sources solves the twin problem of wastage of Raman pump power and providing amplification in U-band. We also performed the simulations of another topology in which a 5m long unpumped EDF was inserted between the first stage and second stage of the EDFA. The backward traveling Amplified Spontaneous Emission (ASE) from the second stage caused the pumping in the unpumped EDF thereby causing signal gain instead of loss. This topology further showed an enhancement in gain of 1-2 dB in the wavelength band of interest (1600-1700nm). The design issue in these topologies is the length of the EDF's. By suitably modeling these lengths, we can obtain appropriate gain profile.
Ultra-high speed optical transmissions require the knowledge of pulse broadening due to higher order dispersion. In this paper, we report the pulse broadening created by Lorentzian input pulse and it is compared with the pulse broadening created by Gaussian input pulse. The pulse broadening due to higher order dispersion terms are obtained for both Lorentzian and Gaussian input pulses. The output optical pulses created by Lorentzian input pulse are compared with the results obtained from Gaussian input pulse. This is followed by the estimation of intersymbol interference (ISI) and the maximum transmission length for Lorentzian input pulse is obtained. It is shown that intersymbol interference strongly depends on pulse profile. Further, the maximum transmission lengths are obtained for both Lorentzian and Guassian input pulses.
Analysis of different loss mechanisms that occurs in photonic crystal fibers (pcfs) is discussed. It is shown that loss appears when these fibers are either joined with another fiber or bent in a radius. The joint losses are obtained for transverse as well as angular misalignments. Peterman spot size definitions are used to define these losses. Bending losses in pcfs are also obtained for different designs of pcfs. It is observed that these loss definitions show dependence on the photonic crystal cladding parameters.
In this paper, the authors have studied the design parameters of a tunable multiple quantum well interference filter. Analogous to the optical thin film filter, an electron wave interference filter is analyzed using the transfer matrix method. The numerical values of the design parameters such as 3-dB bandwidth and quality factor are calculated for various filter configurations with variable number of layers and different thickness values of the film layer for a pass wavelength of 100Å. The tunability of the filter is also investigated.
In this paper, the band structure for 1-D photonic crystal structure, which is composed of two different dielectric layers in a one-dimensional pattern, obtained by transfer matrix method, is reported. It has been observed that the bandgap depends on the contrast of dielectric constant and thickness of dielectric layers. Further, it is found that the enhanced bandgap can be obtained by changing the dielectric contrast and thickness of the layers. Primary & Secondary bandgaps are also estimated and the bandgaps have been engineered with reference to their dependence on spacing between layers and dielectric contrasts. Further, we also report the band gap calculation of three different dielectric layers stacked in 1-D periodic structure. Such structure might find its application in the design & development of asymmetric planar photonic crystals
We report the waveguiding properties of photonic crystal fibers by adapting the effective index method. It has been shown that the waveguiding characteristics can be engineered for different configurations of PCFs. It is shown that the zero dispersion point can be shifted below 1.27?m. Nearly zero dispersion-flattened behavior is observed for a specific combination of cladding parameters of photonic crystal fiber.
In this paper, we have analyzed and simulated the BER performance of a turbo coded optical code-division multiple-access (TC-OCDMA) system. A performance comparison has been made between uncoded OCDMA and TC-OCDMA systems employing various OCDMA address codes (optical orthogonal codes (OOCs), Generalized Multiwavelength Prime codes (GMWPC's), and Generalized Multiwavelength Reed Solomon code (GMWRSC's)). The BER performance of TC-OCDMA systems has been analyzed and simulated by varying the code weight of address code employed by the system. From the simulation results, it is observed that lower weight address codes can be employed for TC-OCDMA systems that can have the equivalent BER performance of uncoded systems employing higher weight address codes for a fixed number of active users.
A great deal of interest has been generated in Photonic Crystal Fibers (PCF) due to its unique propagation characteristics as it offers single mode operation in a wide wavelength range, large mode field diameter and manageable dispersion properties. PCFs are single material optical fibers with a periodic array of air holes running down the length of fiber. The arrangement and spacing of air holes provide freedom to tailor the dispersion properties for telecom applications. Therefore PCFs are expected to be integrated with the existing optical fiber technology. As a result, splicing characteristics of PCF with conventional single mode fiber or with PCF of different air hole spacings, is needed to be evaluated. In this paper, we report the analytical techniques and simulation for the estimation of Splice Loss of PCF with PCF of different geometry, and with conventional fiber. Variation of Splice loss due to normalized transverse offset of two PCFs for different ratios of air hole spacing is obtained. It is observed that the splice loss depends on air hole spacing of PCF and V-value of conventional fibers.
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