Tuesday, January 24, 2006

Week of 1-16-2006

The following project tasks were completed this week:

Followed up with Boulder Nonlinear Systems regarding thier XT and TS shutter systems. Looking at the Bigelow paper, it was found that a maximum carrier modulation frequency of 250Hz is necessary for super luminal propagation. Was put in contact with Kipp Buchart, a solutions engineer at BNS. According to Kipp, BNS shutters elicit a nonlinear response with a linear drive voltage, so to properly operate the shutter for our applications a normal sinusoidal function generator will need to integrate a nonlinear transfer function before driving the shutter. The main issue with using the exisitng BNS shutters is that they elicit a 25 ms total response time corresponding to a modulation frequency of 40 Hz. This will however be sufficient for a signal frequency to be modulated on top of the 250Hz carrier frequency. It was decided between Dr. Blair and myself that this will be used for our low frequency signal modulation frequencies, and that Dr. Blair will speak to the BNS representatives the week of 11-23 at a conference he will be attending in San Jose California.

I also discovered that sinusoidal modulation can be achieved using the original square chopper wheel. This is achieved by taking the chopper wheel with chopping slits just wider than the beam diameter and setting the wheel at an angle such that the edges of the beam are barely clipped by the sides of the chopper wheel. When the wheel spins, an approximation of a sinusoid is achieved. This simple method will be very sufficient to achieve our modulation needs.

This method was implmented in the setup late Friday, and will be tested the following week.

Monday, January 09, 2006

Christmas Break Senior Project Progress

Happy Holidays!

The following is a summary of the main tasks and project progress completed over the break:

- Following coversation with Colorlink Engineering Gary Sharp I spoke with John Korah again. After several back and forth coversations, we discoverd that for the particular application required in my project, the Colorlink LC modulator would not be sufficient. The modulator is a non-linear component, and its retardance level is based on a preset input voltage based off a device characterization table. This would make interfacing the device with the experiement extremely difficult as smooth sinusoidal (analog or fast digital) operatation is essential. Unfortunatley, a good amount of time was spent communicating and planning with Colorlink before this discovery was made. A ColorLink engineer I spoke with recommended looking at a spatial light modulator as a possible solution, and was refered to the vendor DisplayTech.

- DisplayTech's spatial light modulator (SLM) was investigated as a possible solution to achieve sinusoidal intensity modulation without using an expensive electro-optical modulator system (well over $10k). However, upon investigation of the product and corresponence with Dr. Blair, it was found that the SLM offered by Display Tech was a multi-pixel modulation device, and although would work sufficiently for my application, was somewhat of an overkill, as only one large pixel was needed to modulate. Whlie a possible solution, it was determined that a better less expensive method could be used. Product information for this SLM is located at the link below:

http://www.displaytech.com/downloads_04/LDP-0983-HS1-DataSheet.pdf

- At Dr. Blair's prompting, I investigated extensively the use of variable optical shutters in analog modulation. I contacted Kelly Gregorak of Boulder Nonlinear Systems and found information regarding their TS and XT optical shutters. A link to their product information website is included below. The TS shutter offered by BNS seemed ideal, however the driver required must be at least 100V, and if a cheap driver does not exist, a a regular e-o modulator is just as reasonable a solution despite the price. The XT shutter however can use a 20V driver and can operate around 200Hz (which should be sufficient - this will be investigated early in the week of 1 - 09 -06). If BNS can identify a cheap driver, the TS will be used, however if one is not available and the modulation frequencies will work for slow and fast light propagation, the XT shutter will be utilized.

http://www.bouldernonlinearsystems.com/products/opticalShutters/index.htm

- The majority of the break was spent further investigating exisiting solutions to the problem of achieving the neccessary modulation working around cost effective technologies. This proved a fairly formidable task (much more so than I had assumed) however, it appears now that a reasonable solution has been found that fits the necessary specifications and pricing. This task was further complicated by working around the schedules of sales and engineering representatives at vendor companies and their holiday plans. Overall though, I feel that the project has made a significant and necessary step ahead, and with further work, the main goals of creating a robust and operating experiement setup will be near completion soon, allowing time for preparing the experiment for exhibition.

- A link to the main reference for the expermental conditions necessary to achieve slow an superluminal propagation in room temperature Alexandrite crystal is below:

http://www.sciencemag.org/cgi/content/full/301/5630/200