CHAPTER1(RIFAT1)

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CHAPTER 1

INTRODUCTION

1.1Overview

In the recent years, a lot of research has been focused on developing fiber by using Photonic

Crystals (PCs). Photonic Crystals (PCs) are artificial structure in which the periodic variation of

dielectric constant is used to control the flow of light. PCs may be 1D, 2D & 3D crystal

structure. Unlike electronic crystals (which are natural structure) that control the flow of electron

by periodic variation of electron potential and follow Schrdinger equation, PCs followMaxwells equation [1].

Now a day, from the idea of controlling light by means of Photonic Crystal (PC) has led to many

proposals and implementations for novel Photonic Crystal Fiber (PCF). Photonic-crystal fiber

(PCF) is a new class ofoptical fiberbased on the properties ofphotonic crystals.Because of its

ability to confine light in hollow cores or with confinement characteristics not possible in

conventional optical fiber, PCF is now finding applications infiber-optic communications,fiber

lasers,nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas

[2].

This is possible only for Total Internal Reflection (TIR) between the core and cladding region.

The traditional optical fiber having limitations: the fiber has rigid design rules to fulfill: limited

core diameter in the single-mode regime, modal cut-off wavelength, limited material choice

(thermal properties of core glass and cladding glass must be the same). Those traditional

limitations can be overcome by using an array of dielectric rods in air which is the basic concept

of PCFs [2-4].
http://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Photonic_crystalhttp://en.wikipedia.org/wiki/Fiber-optic_communicationhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Fiber-optic_communicationhttp://en.wikipedia.org/wiki/Photonic_crystalhttp://en.wikipedia.org/wiki/Optical_fiber


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CHAPTER-1 INTRODUCTION

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1.2Photonic Crystal

Photonic crystals are periodic dielectric opticalnanostructures that are designed to affect the

motion of photons in a similar way that periodicity of a semiconductor crystal affects the

motion of electrons. Which are composed of periodic dielectric or metallo-dielectric

nanostructures that affect the propagation ofelectromagnetic waves (EM) in the same way as

the periodic potential in a semiconductor crystal affects the electron motion by defining

allowed and forbidden electronicenergy bands.[1]

According to the dimensions of the periodicity, PCs are classified into one-dimensional (1D),

i.e. where the dielectric variation is along one direction. Similarly two-dimensional (2D) and

three-dimensional (3D) PC are defined when the dielectric constant varies along two and threedirection respectively. Schematic samples of different types of PCs are shown in Figure 1.1

[1].

(a) (b) (c)

Figure 1.1: Schematic depiction of three types of photonic crystals (a) 1-D, (b) 2-D and

(c) 3-D. The different colours represent materials with different dielectric constants [1].

Here we have discussed 2-D photonic crystals phenomenon and its spectrum of simulationby the Opti-TDFD simulation software.
http://en.wikipedia.org/wiki/Opticalhttp://en.wikipedia.org/wiki/Nanostructurehttp://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Dielectrichttp://en.wikipedia.org/wiki/Nanostructurehttp://en.wikipedia.org/wiki/Electromagnetic_waveshttp://en.wikipedia.org/wiki/Periodic_functionhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Energy_bandshttp://en.wikipedia.org/wiki/Energy_bandshttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Periodic_functionhttp://en.wikipedia.org/wiki/Electromagnetic_waveshttp://en.wikipedia.org/wiki/Nanostructurehttp://en.wikipedia.org/wiki/Dielectrichttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Nanostructurehttp://en.wikipedia.org/wiki/Optical


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1.3Photonic Crystal Fiber (PCF)

Photonic Crystal (PC) with point defect is used as Photonic Crystal Fiber (PCF) and for a line

defect they are familiar with photonic crystal waveguides (PCW) with more light confinement

and high power transmission than conventional optical fiber and waveguides. PCFs are optical

fibers with a periodic arrangement of low-index material in a background with higher refractive

index. The background material in PCFs is usually un-doped silica and the low-index region is

typically provided by air-holes running along their entire length.

(A) (B)

Figure 1.2: Photonic Crystal Fiber: (A) 2D View and (B) Cross Section View

More specific categories of PCF include photonic-band gap fiber(PCFs that confine light by

band gap effects), holey fiber(PCFs using air holes in their cross-sections), hole-assisted fiber

(PCFs guiding light by a conventional higher-index core modified by the presence of air holes),

and Bragg fiber(photonic-band gap fiber formed by concentric rings of multilayer film).


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1.4 Review of previous works on Photonic Crystal Fiber

The idea of a photonic crystal fiber was presented for the first time by Yeh et al. [1] in 1978.

They proposed to clad a fiber core with Bragg grating, which is similar to 1D photonic

crystal. In 1887, Lord Rayleigh started research on 1-D photonic crystals in form of periodic

multi-layers dielectric stacks and found 1-D band gap. In 1987, Eli Yablonovitch and Sajeev

John published 2 milestone papers concerning about high dimensional periodic optical

structures- photonic crystals. By 1991, Eli Yablonovitch had demonstrated the first 3-D

photonic band-gap in the microwave regime. In 1996, Thomas Krauss made first

demonstration of 2-D photonic crystal at optical wavelength. In 1998, Philip Russell

developed first photonic crystal fiber Photonic band gap diffraction from a periodic structure.

A short overview of PCF development is presented in the bellow:

Table1:Milestone in Photonic Crystal Fiber (PCF)


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1.5

Software

1.5.1 Opti-FDTD Simulator

Opti-FDTD is powerful, highly integrated, user-friendly software that allows computer aided

design and simulation of advanced passive photonic components.

The Opti-FDTD software package is based on the finite-difference time-domain (FDTD)

method. The FDTD method has been established as a powerful engineering tool for integrated

and diffractive optics device simulations. This is due to its unique combination of features, such

as the ability to model light propagation, scattering and diffraction, and reflection and

polarization effects. It can also model material anisotropy and dispersion without any pre-

assumption of field behavior such as the slowly varying amplitude approximation. The method

allows for the effective and powerful simulation and analysis of sub-micron devices with very

fine structural details. A sub-micron scale implies a high degree of light confinement and

correspondingly, the large refractive index difference of the materials (mostly semiconductors) to

be used in a typical device design. [10]

Opti-FDTD used in this thesis for 4 main applications:

1. Layout DesignerThis is where structure and simulation conditions have defined.

2. Profile DesignerThis is used to define the materials and profiles used in the simulation.

3. SimulatorThis program loads the designer file and performs the simulation. The simulator is

started from the layout designer.

4. Analyzer This program is used to view the results and perform some post processing. As

soon as the simulation is done, the simulator will ask if I would like to open the analyzer.

1.5.1 MATLAB R2009b

MATLAB is a software package for high performance numerical computation and visualization.

The basic building block of MATLAB is the matrix. The fundamental data type is the array. It

provides an interactive environment with hundreds of built-in functions for technical

computation, graphics and animation. MATLAB works with its own high-level programming


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language. MATLABs built-in functions provide excellent tools for linear algebra computations,

data analysis, signal processing, optimization, and numerical solution of ODEs, quadrature, and

many other types of scientific computations. There are several toolboxes for special applications.

There is also a help menu which helps us to find description of different function. [15]

MATLAB is used in this thesis for draw different graphs and analysis them.

1.6Research Objectives

The goal and novelty of this research is to

Design, simulation & optimization of Single Mode Photonic Crystal Fiber (SMPCF) and

its dependence on air fill fraction and variation of diameter is analyzed.

The effects of air fill fraction and variation of diameter to the performance of PCF is

analyzed on Dispersion, Confinement losses and Modal analysis.

Finally, the best Single Mode Photonic Crystal Fiber (SMPCF) configuration is designed

for Telecommunication application with 1.5-1.6 m wavelength.

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Outline of thesis

CHAPTER 1: INTRODUCTION:

In this chapter, we introduce photonic crystal, describe photonic crystal Fiber, review

some of the previous works on photonic Crystal Fiber, a short description about software

packages opti-FDTDTM

and its use related to this thesis. Finally, research objective & outline of

the thesis has been given.


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CHAPTER 2: PHOTONIC CRYSTAL FIBER

In this chapter, some basic of Photonic Crystal Fiber (PCF), Guiding Mechanism of light

and Modified Total Internal Reflection in Single Mode PCF, Single-Mode Property , Photonic

Bandgap Guidance, Theoretical Background for light propagation in PCF, Properties of single

mode photonic crystal fibers and its application are discussed.

CHAPTER 3: SIMULATION AND EVALUATION

In this Chapter, the layout design, simulation and mode profile analysis of Photonic

Crystal Fiber (PCF) with Triangular lattice configuration is analyzed with opti-FDTD simulator

and 3D mode Solver.

CHAPTER 4: RESULT AND ANALYSIS

In this chapter simulation result for the different crystal lattice fiber structures is

analyzed. Moreover, Mode Profile, Effective Reflective Index, Dispersion and confinement

losses on the variation of lattice constant and air hole diameter is analyzed .

CHAPTER 5: DISCUSSION AND CONCLUSION

At this chapter, the achievement of these researches has been given with limitations.

Some further works are also proposed for near future.

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