In this episodes Shahriar repairs a Keithley 2500 Dual Photodiode Meter which does not power up. Teardown of the unit reveals two transformers coupled with two fully independent channels. The unit is able to source voltage in two quadrants as well as measure current down to 1-fA resolution. There is also a separate 5V switching power supply responsible for all digital circuits. This power supply is the reason why the unit does not power up. The fault is quickly traced to a bad switching power supply startup capacitor which is easily corrected.

The unit's voltage source & current measurement performance and operation is verified using a LakeShore M81 SSM system coupled with an SMU-10 module:

https://www.lakeshore.com/products/categories/overview/material-characterization-products/measureready-m81-synchronous-source-measure-system/measureready-m81-synchronous-source-measure-system

The Keithley 2500 is also calibrated using the same LakeShore system. An example of active fiber alignment (primary application for the Keithley 2500) is also demonstrated using a pair of infrared LEDs & detectors.

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In this episode Shahriar experiments with a SunPower CryoTel Mini Cryocooler:

https://www.sunpowerinc.com/products/stirling-cryocoolers/cryotel-cryocoolers/ds-2_1

A three-stage turbomolecular vacuum system is used to reach very low pressures of 10E-6 Torr to provide a suitable environment for the cryocooler. Unfortunately, due to the age of this unit, the maximum applied power is limited to 22W. Despite this, reaching temperatures of -210C is possible with no thermal load. A custom heater element is also used to inject thermal energy into the cold tip and measure the available lift from the engine. A new GUI is also developed to control the cryocooler, measure the cold tip temperature, rejection temperature and applied power as a function of time. This allows several cryocooler modes to be explored.

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In this episode Shahriar explores the mechanism and reasons for fiber optic polarization scramblers. The video discusses the many fascinating methods for embedding data onto fiber optic links. Amplitude modulation, phase modulation, dual polarization (MIMO), wavelength division multiplexing, & spatial division multiplexing are all discussed. The overall architecture of typical coherent optical communication systems is also discussed.

With the theory of coherent communication in place, we can dive into the importance & application of such a polarization scrambler instrument. We further dive into how the unit works followed by a complete optical test system which characterizes the polarization scrambling capabilities. Lastly, a complete teardown shows the ultrasonic, multi-segment transducers which induce birefringence on the fiber segment and cause polarization scrambling.

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