COMSOL MULTIPHYSICS SOFTWARE

sxb5542@rit.edu Saivivek Bheemanathini

Introduction

Started by grad student Germund Dahlquist based on code

developed for a grad course at Royal Institute of Technology in

Stockholm, Sweden

Its earlier version was also called as FEMLAB (Finite Element

Method) software

Provides simulation environment for real world applications

Finite element analysis, solver and simulation software package for

Multiphysics phenomena

Capabilities

Interactive modeling and simulations using FEM

Pre-defined physics, user defined equations in GUI (Graphics User

Interface) and unlimited physics combinations

High performance numerical algorithm, powerful post processing

capabilities and extensive model libraries

Bi-directional interface to Matlab and Simulink

RF module and optical structure engineering that can be easily

combined with other module

Modeling optical coupling between laser

waveguide and optical fiber

Schematic Design

Design

Laser Waveguide

Co-axial Cable

Optical Fiber

Thought Process

Model the coupling between waveguide and co-axial cable

Design the waveguide to meet the needs of Laser properties

Since there is no pre-defined waveguide for laser and optical fiber, RF waveguide is considered for the initial start-up and optical fiber is designed

COMSOL software deals with PDE (Partial Differential Equations) in finite element analysis

PDE for the electro-magnetics are studied and applied

Design the coupling between waveguide and optical fiber including the effects of stress and thermal distribution

Design steps

Define Geometry-

Select space dimension- 1D, 2D, 3D

Draw the feasible design in a graphical window

Add physics

Select Radio-Frequency module

Electromagnetics-Frequency domain (emw)

Select Study type-Results

Frequency domain, Stationary and Time independent

Design

Modeling between the co-axial cable and RF waveguide is done

Design

Variations of electric field intensity along the waveguide in

frequency domain is obtained

Modeling between waveguide and optical fiber

Since there is no optical fiber pre-defined template, it is constructed by

using two hollow cylinders and adding materials to differentiate the core and cladding of optical fiber

Following parameters are considered for the design

H 1[mm] Height, waveguide

L 10[mm] Length, waveguide

L 3[mm] Length, coaxial cable

R 0.25[mm] Outer radius, coaxial cable

r 0.125[mm] Inner radius, coaxial cable

R1 125[um] Cladding radius, optical fiber

R2 8[um] Core radius, optical cable

R.I core = 1.45, R.I cladding = 1.43

Design

Material properties are added to the design

Design

Results

Variations of electric field intensity along the waveguide in

frequency domain is obtained

Things that have gone wrong

Since there is no laser waveguide pre-defined template, RF waveguide is considered for the initital start-up

RF waveguide deals with the frequency of radio waves, i.e. 40 GHz whereas optical fiber deals with the frequency of THz.

Hence there in no efficient coupling between waveguide and optical fiber in frequency domain

This phenomena is clearly explained in the previous slide as there is no variations in the electric field intensity along the waveguide and optical fiber

Although the design is perfect, boundary conditions and partial differential equations are critical to deal with the design

Corrections that may lead to the success

Design the waveguide by applying proper boundary conditions and

partial differential equations of electro-magnetics to activate the

laser properties

Apply the equations of wave optics for the propagation of light

inside the waveguide

Add physics-

Heat transfer: which is essential for understanding the thermal

distribution in the process of coupling between the waveguide and

optical fiber.

Corrections that may lead to the success

Add physics-

Structural Mechanics: Adding thermal stress to the design helps us to understand the real world scenario how stress act as an impairment and

optimize the design to get maximum performance

Good understanding of COMSOL tool to exercise the transition

from the raw design to the end product and optimizing the design for

the user advantages and objectives.

REFERENCES

1. COMSOL manual, Introduction to COMSOL Multiphysics, v 4.3a, Jan 2013

2. COMSOL software- Wikipedia, http://en.wikipedia.org/wiki/COMSOL Multiphysics

COMSOL website, http://www.comsol.com/