Monday, March 20, 2006

Week of 3-6-2006

The following specific project tasks were completed this week:

-At the suggestion of Dr. Blair, the addition of a 1/4 waveplate into the LC modulator/cross polarization device was investigated. Such a device would initially circularly polarize incident light when placed before the first polarizer. This would allow for the LC cell control voltage to create a 50% attentuation level corresponding to zero drive voltage.

-Below are links ound for possible 2" square 1/4 waveplates. Two options are available, zero order and multi order. Zero order waveplates have a retardance that is less dependant on wavelength than multi order. Since the system currently in the setup operates at specific wavelengths, a zero order waveplate is not a necessity. Polymer film waveplates were also investigated with similar, and are likely to be used due to their relativly cheap cost. These are available from a mail order vendor.

- The oritentation of the current cross polarizer/lc cell setup was optimized resulting in the configuration with polarizers oriented perpendicularly to LC cell. This configuration provides the highest modulation contrast between off and on states as well as best sinusoidal response.

- Optics in the final system were cleaned and room was left for the later addition of a 1/4 waveplate device. Testing began using a solid state ruby rod to try to achieve slow light propagation behaviours. Proper stable modulation was achieved, however, the laser used was operating at approximately 200mW, slightly less than earlier testing, and slightly too low to accurately achieve propagation delay. To achieve higher output power, the laser with need tuning.

1/4 Waveplate links:

Thorlabs:
Zero Order
Multi Oder:
Melles Griot:
Mica Plate
Quartz Plate:

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