Dispersion

Question 1

What is a monochromatic plane wave?

Answer 1

Is a sinusoidal signal that has no beginning or end (i.e. idealized function that runs from negative to positive infinity in time. It operates at one frequency and has no spectral width.

Question 2

What is the temporal Guassian pulse model?

Answer 2

Its a great analytical tool for understanding the impact of dispersion on pulse propagation

Question 3

What are the two components of an electric field?

Answer 3

1) Envelope: Gaussian pulse shape

2) Carrier: Plane wave at optical frequency (w0)

Question 4

What type of detector is used?

Answer 4

Square log detectors, and they detect the intensity of a signal.

Question 5

What is the common material found in fibers, sand, refined sand?

Answer 5

Fused silica. Its used because its very abundant material.

Question 6

What is dispersive media?

Answer 6

is media in which the index of refraction is a function of frequency. As we saw in the previous lectures, photonic devices typically operate in the transparent spectral regions of the optical materials used in photonics and all of these materials are dispersive in these spectral regions.

Question 7

What is group velocity?

Answer 7

The velocity of the pulse itself

Question 8

What is the impact of pulse propagating in a dispersive media?

Answer 8

1. Pulse propagates at an average group velocity, vg
2. Pulse broadens due to group velocity dispersion (wavelength dependent group velocity).
3. Pulse chirps due to group velocity dispersion (different frequencies arrive at different times)

Question 9

What is group velocity?

Answer 9

it describes the speed of propagation of a pulse of light and represents the velocity of transport of pulse energy. Its derived by the superposition of two sinusoidal waves with slightly different frequencies, and use a trig identity, you get an expression of the electric field which can represent the carrier and delta envelope.

Question 10

What does group velocity represent?

Answer 10

It represents the velocity of the envelope.

Question 11

What is phase velocity?

Answer 11

The velocity of the peak of the carrier waveform.

Question 12

Phase slippage is what?

Answer 12

Its when phase velocity moves inside of the envelope

Question 13

What is needed to find the relationship of frequency differences with wavelength?

Answer 13

You need to take the derivative of the wavelength.

Question 14

What is the derivative of the refractive index?

Answer 14

In some media, that media is equal to zero and the common example is if your propagating in a vacuum such as space, and there is no media that has dispersion, so the term is zero so the group velocity is equal to the phase velocity.

Question 15

The group velocity can be expressed as the __________

Answer 15

Group Index

Question 16

What is Group Velocity Dispersion (GVD)?

Answer 16

Is a property of how much broading occurs with a pulse as it goes through a medium. So we are looking at the delta-tau. We know our time domain (tau) and if we take the derivative of that with respect to lambda, you go through the math where it simplifies by the second derivative of the refractive index curve. You can look at