Advanced Undergraduate Laboratory

Department of Physics

University of Toronto

LPP: Linear Pulse Propagation and Dispersion

Also known as the "Acoustic Waveguide", this experiment is designed to introduce the physics of waveguides and dispersive pulse propagation. A set of speakers drives sound pulses down different modes of an acoustic waveguide, and the student studies what the system (differential equation plus boundary conditions) imposes on the pulses. This a good prototype for light propagating in optical fibres and the chirped pulse compression and amplification methods used in ultrafast lasers, radar, and sonar.

Write-Up in PDF Format or Microsoft Word Format.

(The experiment is currently located in MP246; last major write-up revision: September 2020.)

Some additional resources:

Some possibly useful Labview files. To run these programs you must have Labview installed on your computer. If you don’t have Labview, you can get a free program for running (but not developing) Labview programs from the National Instruments web-site: Search for "LabVIEW Run-Time Engine", or try this link for the 2018 Windows version. (Mac and Linux versions are also available.) You must register, and then the Run Time Engine is free to download and install.

This experiment is part of the Photonics/Optics Teaching Laboratory at the Department of Physics, UniversityToronto

Photo of experimental setup.

Here is the experiment setup, showing the 6 metre long waveguide, and the computer which runs the speakers and microphones.

Photo showing view down the waveguide.

Here is the view down the waveguide.

A sample data plot showing effects of dispersion on pulse.

This plot of pulse intensity versus frequency (vertical axis) and time (horizontal axis) shows the affects of dispersion on the pulse. Data taken by Kevin Hurley on January 31, 2006.

A sample data plot showing delay increasing as frequency approaches the cutoff.

Another beautiful chirp plot: intensity at each frequency and time (both arbitrary units) show delay increasing as frequency approaches the cutoff. Data taken by Benjamin Leung, March 2006.

Last updated on 14 September 2020