Sandia

Question 1

Describe the features in a probe station.

Answer 1

Needle-like probes connect wires that carry voltage/current to “bond pads” on a semiconductor device that allow for voltage/current to pass through with negligible resistance. Can be translated in X,Y,Z to land at the center of gold (for GaAs) or aluminum (Si) pads. XYZ stage plus probe is called a micromanipulator.

Question 2

Describe a Sagnac interferometer.

Answer 2

It was what we used to measure linewidth of VCSELs. Forward and reverse paths don’t overlap as they do in a Fabry-Perot.

Question 3

How does a ring resonator work?

Answer 3

Light of the right resonance (based on TIR) gets passed from a bus waveguide through a loop where it builds intensity over multiple round trips due to constructive interference, then output to an output bus waveguide; only a few wavelengths are at resonance within the loop so it functions as a filter.

Question 4

Applications of ring resonators?

Answer 4

Optical multiplexing; MEMS tunable microring resonators for use in wavelength division multiplexing applications

Question 5

What’s wavelength division multiplexing?

Answer 5

Technology that multiplexes multiple optical carrier signals of different wavelengths through an optical fiber, allowing for higher throughput. Setup is a multiplexer at the transmitter, the fiber, then a demultiplexer at the receiver.

Question 6

Example of passive vs active optical components?

Answer 6

Passive: waveguides, gratings, etc. Active: semiconductor laser, waveguide modulator (driven by current)

Question 7

What are tapeouts?

Answer 7

Tapeouts refer to the process of finalizing an integrated circuit design into a final .GDS file that gets converted into several mask plates for doing photolithography; KLayout is used.

Question 8

What do RTL and TIA stand for?

Answer 8

Register Transfer Level, a method of modeling digital circuits in terms of flow of digital signals, is basically code for circuits. 
(or) Resistor-transistor logic, class of circuits using BJTs as switches. 

Transimpedance amplifier, current to voltage converter, implemented with op amps. Gain is set by a feedback resistor (100k ohms)

Question 9

What is impedance matching?

Answer 9

Matching source and load impedances to minimize signal reflectance or maximize power transfer.