Nonlinear

Question 1

What is group velocity vs phase velocity?

Answer 1

Group velocity = velocity of an entire group of waves (bulk superimposed wave), phase velocity = that of one of the peaks of the wave.

Vg = Vp - Lambda * dVp / dLambda

Question 2

Applications of photonic crystal fibers

Answer 2

Dispersion (nonlinear interactions), reflectance, supercontinuum generation

Question 3

Kerr effect / Pockels effect

Answer 3

Change in refractive index with due to applied electric field. Kerr effect is nonlinear (prop to E^2), Pockels is linear.

Question 4

What’s self-phase modulation and what is it used for?

Answer 4

Ultrashort light pulse gets refractive index change due to Kerr effect, causing phase shift in pulse, causing change in frequency spectrum. Used for spectral broadening (if un-chirped or up-chirped), used for compression if initially downchirped.