DSpace Collection:

Application specific design of photonic crystal fibers, waveguides and devices

2018-01-01T00:00:00Z

Title: Application specific design of photonic crystal fibers, waveguides and devices Authors: Boruah, Jiten Abstract: Photonic Crystals (PhC) are micro-structured materials with periodic variation of dielectric constant in one, two, or three dimensional length scale and periodicity comparable to the wavelength of light. Because of the periodicity, the PhC exhibit strong reflection for a range of wavelengths resulting in the formation of Photonic Band Gap (PBG). By selecting an appropriate crystal structure of certain materials, one can get a PBG or a frequency range in which propagation or existence of electromagnetic waves is forbidden. Light with frequency that falls within this forbidden frequency range or PBG can be guided through such PhC by creating a waveguide. Similarly, light can be confined or trapped inside such a PhC by creating a cavity. The confined modes of a photonic cavity could be used in optical resonators, laser cavities, filters, switches, demultiplexers, sensors etc. Waveguide and cavity can be created by introducing defects in the periodic structure of PhC on different platforms like Silicon Carbide (SiC), Gallium Arsenide (GaAs) etc predicted for use in all optical networks. The most significant application of PhC is the design of a novel waveguide known as Photonic Crystal Fiber (PCF) which is essentially a fused silica optical fiber with a periodic distribution of voids or air holes in the cladding that run parallel to its axis. PCF has the extraordinary ability to carry more light in the core, confinement characteristics not possible in conventional optical fiber and characterized by simpler and economic fabrication technique. Nowadays, PCF is finding applications in optical fiber communications, fiber lasers, nonlinear devices, high-power transmission, and highly sensitive gas sensors. Since its inception, PCF is mainly fabricated from silica glass material. But today, researchers have been profusely using materials like fluoride glass, polymer-based and chalcogenide glass in fabrication of PCF. Use of these materials in PCF offer advance characteristics like high non-linearity, high refractive index, high mode confinement, Raman amplification etc. In this thesis, first, introductions of PhC and PCF have been given and discussed regarding PhC and PCF based devices. This is followed by detailed discussion of theory of light guidance through PhC and PCF, Photonic band gap engineering in PhC, analysis of PhC and PCF structures and different PhC and PCF fabrication methods. Computational methods utilized in the analysis of PhC and PCF including an overview of the thesis work have been discussed in the introduction. Investigating photonic structures which are less sensitive to environmental fluctuations like temperature is a valuable area of research. Here, in this thesis, it has been proposed to design photonic crystals using temperature resilient material Silicon Carbide (SiC) and study the variation of width of photonic band gaps in SiC photonic crystals with change in temperature and a comparison with Silicon (Si) photonic crystals using Plane Wave Expansion (PWE) method. Further, SiC point defect cavity has been created in the PhC and analysis of the SiC photonic crystal cavity defect modes have been carried out using Finite Difference Time Domain (FDTD) method. The effect of temperature on different parameters of the proposed designs like band gap width, defect cavity mode dispersion, the resonance mode and quality factor of resonant mode have been studied. The SiC PhC devices can be used for high temperature and power transmission which is difficult to achieve with conventional Si or GaAs based photonic crystals and devices. Apart from applications in optical communication, various other SiC based devices such as optical filters, switches and lasers etc can be designed. The SiC based devices are stable at high power and high temperature, at which the silicon based devices, cannot sustain such high power and temperature. Apropos of the recent trend of using new fabrication material in PCF, in this thesis, the application specific design of PCF having solid core with regular and irregular cladding geometries, using different and new material and doping the cladding have been studied. First, the design of a PCF in Fluoropolymer material has been done and analyses of the proposed PCF has been carried out in terms of the parameters like effective refractive index of the guided mode and dispersion for wavelength range 10μm to 300μm using full vectorial Finite Element Method (FEM) and MATLAB computational tool. The transmission characteristics of Fluoropolymer PCF are found to be comparable with the earlier published result. The proposed Fluoropolymer PCF may find applications in long distance telecommunication and in mid-infrared region. Next, the design of a PCF with irregular cladding geometry has been proposed. The PCF has been named after its W letter shaped refractive index profile as W-type PCF. The analysis of the proposed W-type PCF have been done in terms of the parameters like bend loss of the guided mode, effect of temperature on bend loss and nonlinearity using full vectorial FEM . The transmission characteristics of W-Type PCF obtained are found better compared with the earlier published results. The power coupling in W-type PCF is more compared to conventional PCF. The bend insensitive nature of the proposed W-type PCF structures makes them good candidate for large mode area fiber design and fit for fiber to home applications. Then, cladding doped large mode area W-type photonic crystal fibers are designed. The analyses of these proposed structures in terms of the parameters like confinement loss, effective refractive index of the guided mode, bend loss, birefringence, sensitivity, effective area and non-linear co-efficient using full vectorial FEM have been carried out. The proposed W-type PCF structures found to possess very low confinement loss and low macro bend loss. The W-type PCF is found to be birefringent and sensitive and can find application in telecommunication and sensing. In addition to the above proposed PCF structures, a PCF structure has been designed for nonlinear applications in novel Ga-Sb-S based chalcogenide glass which is a different and new PCF fabrication material. The propagation characteristics of the designed Ga- Sb-S based chalcogenide glass PCF structure like effective refractive index of the guided mode, dispersion, effective area, non-linear co-efficient have been investigated by employing full vectorial FEM and MATLAB computational tool. The transmission characteristics of Ga-Sb-S-PCF have been obtained for wavelength range 0.8μm to 14μm. The nonlinear coefficient as high as 14.92 W-1m-1 with effective mode area of 3.37μm2 at the operating wavelength of 1.55μm for the proposed photonic crystal fiber structure has been found. The proposed PCF structure exhibit flat and low dispersion value between spectral spanning 2.4μm - 2.7μm with maximum dispersion variation of 20 ps/nm km. The PCF structure possesses zero dispersion wavelength value at 2.6μm. This novel Ga-Sb-S material based PCF structure has been studied for the first time since the inception of the novel material Ga-Sb-S and can be a promising candidate for nonlinear applications such as mid-infrared supercontinuum generation, slow light generation, and mid-infrared fiber lasers. In the last, the thesis includes summery and future scope of the research work reported.

Experimental studies of c and d waste as a geo material for road construction

2016-01-01T00:00:00Z

Title: Experimental studies of c and d waste as a geo material for road construction Authors: Goel, Rajiv Abstract: The present work proposes a framework for recycling of construction and demolition waste(CDW) as geo-material for construction of sub base and base course of flexible pavement. It was based on the results of experimental studies of physical and engineering properties of recycled CDW aggregates compared to standard requirements as per MoRTH (Ministry of Road Transport & Highways) specification of road and bridge works (2001),which was supported through field testing and performance evaluation of 3 km trial stretch of road constructed using recycled waste. The physical and engineering properties like specific gravity, grain size distribution, density-moisture relationship by Proctors compaction test, aggregate crushing value, Los angles abrasion value test, and California bearing ratio (CBR) of recycled CDW aggregates have been tested in laboratory and compared with that of new virgin materials as specified in codal specification. It is observed that most of the physical and engineering properties of recycled CDW aggregates fulfil the standard code specification else the effect of variation of property has been analysed and suitable remedial proposals are incorporated in the proposed frame work. The CDW aggregates have variable characteristics as they are extracted from diverse spectrum of materials used in old buildings and structures. This frame work suggests laboratory tests to assess the variation in quality of waste aggregates and suggested the parameters for design of flexible pavements layers using waste materials. The field investigation and performance evaluation of trial stretch designed as per codal provisions using CDW aggregates, has been carried to investigate the effect of use of this waste as sub-base and base course. Thereafter the performance of sub-base and base course was evaluated through field testing of density of compacted pavement, relative density and relative compaction, plate load test of compacted pavement for assessment of settlement on application of loads and modulus of sub grade reaction. The safe bearing pressure from plate load test at the settlement of 1.25 mm has been found in the range of 450-650 kPaat the top of base course, without the laying of bituminous layers of 130mm thickness. These layers further contribute to the load bearing capacity of pavements. As the permissible axle load in India is 100kN, it can be safely assume that this pavement even with the impact of moving wheel loads may not cause structural failure. The pavement performance monitoring and evaluation has been carried out for a period of seven years and compared with normal maintenance requirements of typical flexible pavement. The comparison has revealed that the performance of flexible pavement constructed using CDW aggregates is comparable to the natural aggregates. The present work proposed a frame work for recycling of CDW aggregates in flexible pavements in the form of systematic flow charts and a step by step methodology for utilisation of CDW in field as an economically viable and environmental friendly material with partial or full substitution of standard natural materials in construction of flexible pavements.

Role of special feature in side resistance of a model steel pile

2015-01-01T00:00:00Z

Title: Role of special feature in side resistance of a model steel pile Authors: Kumar, Naresh Abstract: The steel piles have the advantages of being robust, light to handle, capable of carrying high compressive and tensile loads when driven to a varied stratum, capable of being driven to a deep level to reach a bearing stratum and to develop a high frictional resistance, although, their cost per metre run is relatively high compared with precast concrete piles. The frictional resistance of pile is known as side resistance of pile in the literatures on piles.The main contribution of this work to the body of knowledge is introducing invented special feature which resulted in increase in side resistance of a model steel pile and that, too, with almost minimum disturbance of the soil (air and sun dried sand has been considered in the present wok) while introducing a special feature. Described herein is a slotted holes, mesh-filtered; mesh-plugged steel pile (patented by Kumar and Trivedi, 2013a, b) having a pattern of regular or zig-zag orthogonal spikes (spiking out from the lateral surface of the pile in orthogonal or in inclined direction at varied angles) that can be used in a variety of soil conditions as well as in apparatus and associated methods. In saturated and submerged soils (pore pressure measurements are not considered in the present thesis), slotted holes helps in increase of effective stresses in soil-steel pile surface interaction by draining out extra build-up of pore water pressure in the immediate and longer run of time under the structural loading pressure. Flow of water at higher potential will not be outwards from the lateral surface of the steel pile, but, inwards to inside of steel pile through slotted holes of steel pile. These slotted holes are on the entire lateral surface of steel pile except conical surface at the bottom of steel pile. It reduces the chances of build-up of excess pore water pressure for liquefaction of soils in the radial stressed zones of interaction of soil-steel pile. As effective stresses are directly proportional to shear strength of the soil mass so, any reduction of pore water pressure through slotted holes of mesh- filtered steel pile or lead to increase of side-resistance on soil-steel pile surfaces. The side-resistance which is a part of load carrying capacity of steel piles tend to increase to a large extent due to increase of effective stresses on soil-steel pile interface. This is further increased due to presence of slotted holes on the outer lateral surface of the steel pile which not only drains out pore water to inside of the steel pile through mesh filter slotted holes, mesh-filtered; mesh-plugged steel pile but also increase frictional forces due to roughness induced on the surface. Further, this work considered the effect of orthogonal as well as inclined spikes, which in totality due to interlocking arrangement of spikes with the soil, lead to increase in side resistance. The whole arrangement of providing slotted holes, spikes along with doubly sloped circular fins on lateral surface at regular intervals, increased the side resistance of the steel pile, increased the density of adjoining soil mass, and consolidated the soft soil, thereby, improving the safety factor for designed loads of super-structures, making it usable for construction of deep foundation unit. The dewatering unit (not discussed in this thesis) as patented by Kumar and Trivedi (2013 a, b)is attached through a pipe from the top-most slotted hole of the steel pile which act to remove the drained out water collected in-side the conical-tip of slotted hole-cum-spiked steel pile. This special feature of slotted holes-cum-spikes was provided throughout the vertical lateral surface of the model steel pile. This work has introduced an improvement factor, ξ, which numerically captures the potential increase in the load carrying capacity of a model steel pile in the context of in side resistance due to special feature i.e. slotted holes, spikes and fins. The side resistance increased due to length of spike, diameter of spike and inclination of spike (maximum at 60º in the direction of application of force). The following parameters were kept fixed w.r.t. number of spikes, spacing between the spikes in a row, vertical spacing between the spikes, pattern of the spikes (i.e. zig-zag or regular pattern), shape of the spikes (cylindrical), taper of the spikes (0º in the present work because of cylindrical spikes), surface roughness of the spikes in the form of threaded pattern on the surface on the spikes coming through welded nuts. The spike inclination, β, w. r. t. vertical plumb line is defined as any angle at a point on a model steel pile between outside upward plain surface of a model steel pile and inclined spike and varies in the range 0º< β <180º for the vertical direction at specified constant angular intervals of 30º, where β=30º, 60º, 90º, 120º and 150º) were considered in increasing order in the clockwise direction when spikes were to be seen on the right of the vertical axis of upright direction of the model steel pile. There was an increase in side-resistance of a model steel pile which leads to significant increase of load carrying capacity of the model steel pile. Providing a special feature such as, whole arrangement of providing slotted holes, spikes and that, too, at various inclinations from 30º to 150º, along with doubly sloped circular fins on lateral surface at regular intervals, on a model steel pile, not only increased side resistance but also increased load carrying capacity of a model steel pile. It made the specially featured i.e. slotted-cum-spiked-cum-doubly sloped finned (facing vertically upwards) model steel pile is not only a user-friendly but an economical one also (due to lesser overall cost of per meter run of a special featured steel pile when compared for an equivalent load carrying capacity of per meter run of a plain model steel pile).

Characterization of photonic crystal fibers and metamaterials theory and experiments

2015-01-01T00:00:00Z

Title: Characterization of photonic crystal fibers and metamaterials theory and experiments Authors: Kishor, Kamal Abstract: Recent developments in optical technologies are being shifted towards nano-scale devices of sub-wavelength dimensions. In these emerging technologies photons are being manipulated and controlled using devices having unit cells with a dimension in wavelength range or even with a dimension smaller than wavelength. Photonic crystal and Metamaterials are the prime focus area of research in photonics in the past few years with the number of publications and patents increasing exponentially. Photonic crystals are patterned materials with a well defined periodicity in dielectric constant. Photonic Crystal Fibers (PCFs) are one of the most important applications of photonic crystal materials. PCF is an optical fibers made up of single material with an arrangement of periodic air holes across the cross-section running down its entire length. PCF has the ability to confine light with the confinement characteristics, not possible in conventional optical fiber due to its high degree of design flexibility. Metamaterials are the specially designed structures having negative permittivity and permeability simultaneously at the same operating frequency for which the electromagnetic wave shows anomalous behaviour, i.e. phase and group velocity would be in opposite direction. Metamaterials provide precise control over the flow of electromagnetic waves. It is now the critical phase of their development as they move fast from the realm of fundamental studies to the manufacturing of photonic devices and commercial deployment in optical communication network. For the extraction of optimum performance of any designed structure it is the important to characterize it in terms of its waveguiding, geometrical and transmission parameters. In this thesis first the characterization of Endlessly Single Mode (ESM) PCF from its Far Field intensity measurements has been explored. The characterization results are verified and supported with experimental as well as simulation results. From the experimental measurements of the far field intensity pattern, we obtained the transmission characteristics of ESM PCF in terms of V-number, effective refractive index of the cladding, radius of the core, numerical aperture, etc. The experimental values of the waveguiding and geometrical parameters are found to be in agreement with the simulation results obtained using Improved Effective Index Method (IEIM) and Scanning Electron Microscope (SEM) data. Further, characterization of a specially designed Polarization Maintaining (PM) PCF has explored using Far Field intensity distribution pattern. It is observed that the waveguiding and geometrical parameters obtained from the far field measurement of PM PCF match with the manufacturer/simulation/SEM data within the experimental limits. Thus, this characterization method provides a useful tool for online characterization of PM PCF. Next, a V-shaped SRR metamaterial has been fabricated and characterized. The fabricated structure has shown a unique property of angular-gap-dependent tuneable negative refractive index (NRI) characteristics. The unique property of this structure is that by varying the angular gap between its arms, the capacitance (C) for the structure can be changed, and hence there can be a great control over the NRI. It is experimentally and computationally investigated the interdependence of the capacitance (C) and inductance (L) of the structure, and it is observed that by changing the angular gap of V-shaped SRRs, it is possible to control/tune their NRI at the corresponding resonance wavelength. After the tunable metamaterial structure next is to design of a split ring resonance (SRR) based planar metamaterial to achieve the negative refraction in optical communication window. A “I” shaped split ring resonator (SRR) metamaterial designed has been explored. This metamaterial design is showing negative refraction in the optical communication window around wavelength of 1.5 μm. Further the structure is characterized using finite differential time domain (FDTD) method in terms of its propagation characteristics. All the key electromagnetic parameters i.e. such as permittivity (ε), permeability (μ), refractive index (n) etc have been obtained from the simulation data obtained for propagation characteristics for the structure. The electromagnetic parameters (such as permittivity (ε) and permeability (μ)) as well as the refractive index for the reported structure are negative in broad optical communication window of 1.4μm to 1.6μm.