1) Class Reviews
If you sum up light transmission, absorption and scattering doyou get unity (1)? If yes why, if not what is missing?
In your owns words describe the difference between phase andgroup velocity
From Maxwell’s equations derive the wave equation. Stateexplicitly any assumption you
made.
How is the beating length defined of a directional coupler.Explain in your own words why a
symmetric coupler is needed to fully switch a signal from across-to-bar output and a
asymmetric one cannot be used?
2) Laser Analysis
a) Calculate the threshold gain of a double heterostructure (DH)edge emitting laser with an intrinsic loss a?i = 20 cm-1. Assume anoverlap factor of G? = 20%. The laser is 100 um long, and the gainmedium’s index refractive index is comparable to that of Silicon.Assume both facets have an equal reflection of R = 40% and outsideis air.
b) Find the threshold carrier concentration N for an opticalgain of g(N) = a(N-Ntr), where a = 1500 cm-1, and Ntr =1016cm-3.
3) Modulator
Draw the bands for a Quantum Confined Stark effect. How does theoptical signal modulation created?
State the equation for a phase shift-based modulator. A figureof merit (FOM) is to create a small Vp?L, meaning a small devicelength and low voltage to get to a p?phase shift. Name 3 designoptions to improve (reduce) this FOM.
4) Photodetector
In a PN junction where is light absorbed? Meaning a) in theflat-region on the p-side, or b) on the flat region on the n-side,c) neither of those, but in the deleted region where the bandsbend?
Use your answer from before to explain why a P-i-N photodetectoris a ‘better’ photodetector than a PN junction.
Calculate the photo-current for a detector with an quantumefficiency of 90%, a gain of 100, a responsivity of 0.7 A/Wreceiving an input power of 5mW
