ee 230 optical fiber communication lecture 2
Download
Skip this Video
Download Presentation
EE 230: Optical Fiber Communication Lecture 2

Loading in 2 Seconds...

play fullscreen
1 / 22

EE 230: Optical Fiber Communication Lecture 2 - PowerPoint PPT Presentation


  • 102 Views
  • Uploaded on

EE 230: Optical Fiber Communication Lecture 2. Fibers from the view of Geometrical Optics. From the movie Warriors of the Net. Total Internal Reflection. Reflection as a function of angle. The reflectivities of waves polarized parallel and perpendicular to the plane of

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' EE 230: Optical Fiber Communication Lecture 2' - malo


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
ee 230 optical fiber communication lecture 2
EE 230: Optical Fiber Communication Lecture 2

Fibers from the view of Geometrical

Optics

From the movie

Warriors of the Net

reflection as a function of angle
Reflection as a function of angle

The reflectivities of waves polarized

parallel and perpendicular to the plane of

incidence as given by the Fresnel equations

This additional Phase Shift is not accounted for in geometrical wave approach

Fiber Optics Communication Technology-Mynbaev & Scheiner

principal types of optical fiber
Principal Types of Optical Fiber
  • Types of Fibers
    • Single mode/Multi-mode
    • Step Index/Graded Index
    • Dispersion Shifted/Non-dispersion shifted
    • Silica/fluoride/Other materials
  • Major Performance Concerns for Fibers
    • Wavelength range
    • Maximum Propagation Distance
    • Maximum bitrate
    • Crosstalk

Understanding Fiber Optics-Hecht

fabrication of optical fiber
Fabrication of Optical Fiber
  • Fabrication of fiber preform: macroscopic version with correct index profile
  • Drawing of preform down into thin fiber
  • Jacketing and cabling
step index fiber
Step-Index Fiber
  • Cladding typically pure silica
  • Core doped with germanium to increase index
  • Index difference referred to as “delta” in units of percent (typically 0.3-1.0%)
  • Tradeoff between coupling and bending losses
  • Index discontinuity at core-clad boundary
basic step index fiber structure
Basic Step index Fiber Structure

Fiber Optics Communication Technology-Mynbaev & Scheiner

ray trajectories in step index fiber
Ray Trajectories in Step Index fiber

Meridional Rays

Skew Rays

coupling light into an optical fiber
Coupling Light into an Optical Fiber

Fiber Optics Communication Technology-Mynbaev & Scheiner

acceptance angle
Acceptance Angle

The acceptance angle (qi) is the largest incident angle ray that can be coupled into a guided ray within the fiber

The Numerical Aperature (NA) is the sin(qi) this is defined analagously to that for a lens

Optics-Hecht & Zajac

slide11

n0

θ2

θ1

φ2

φ1

nCO

nCL

numerical aperture
Numerical Aperture

From Snell’s Law,

For total internal reflection, θ2=90º

What value of φ1 corresponds to θc?

That is the maximum acceptance angle for the fiber.

φ2 = 90º-θc sinφ2 = cos θc

, so

Again from Snell’s Law,

(= NA), so

for corning smf 28 optical fiber
For Corning SMF-28 optical fiber

nco=1.4504, nCL=1.4447 at 1550 nm

NA = 0.13

Acceptance angle = 7.35 degrees

geometrical view of modes
Geometrical View of Modes
  • Ray approximation valid in the limit that l goes to zero
  • Geometrical Optics does not predict the existance of discrete modes
  • Maxwells Equations and dielectric boundary conditions give rise to the requirement that the fields and phase reproduce themselves each “cycle”

Fiber Optics Communication Technology-Mynbaev & Scheiner

origin of modal dispersion
Origin of Modal Dispersion
  • Straight path along fiber axis has distance L and velocity c/nCO for transit time of LnCO/c
  • Path at maximum acceptance angle φc has distance L/cosφ2 where φ2=90º-θc and thus a longer transit time.
  • Transit time difference equal to
  • Dispersion limits rate of signals that fiber can handle
  • If spread can be up to 70% of bit period, then maximum bit rate is 1.4cnCO/L(NA)2
intermodal dispersion
Intermodal Dispersion

Fiber Optics Communication Technology-Mynbaev & Scheiner

bandwidth for various fiber types
Bandwidth for Various Fiber Types

No intermodal time shift for single

Mode Fiber

Fiber Optics Communication Technology-Mynbaev & Scheiner

graded index fiber
Graded Index Fiber

Fiber Optic Communication Systems-Agarwal

Fiber Optic Communications-Palais

ray propagation in graded index fiber
Ray Propagation in Graded-Index Fiber

Graded Index Slab Uniform in X and Z

Fundamentals of Photonics - Saleh and Teich

comparison continued
Comparison, continued

If NA=0.13 and nCO=1.45,

∆tSI/L=19 ps/m

∆tGI/L=0.039 ps/m

Graded-index fiber has substantially less modal dispersion

ad