Lol not sure the best place but I don't think the 3000usd+ community knows much about diy repairs.
It's likely just a clear linear pol but I cant say without seeing it.
As for why it's there, it is THE reason LCD works. Incoming light is polarized. LCD alters the polarization in a pixel by pixel basis. Then output light is filtered with another polarizer, thus producing black and white pixels.
That's why when u took it out, the entire image became blue, as the lcd no longer had control without polarized input.
There is no particularly good site that consolidates all this. I learned as u did, from taking things apart, reading various articles, forums.
As for contrast ratio, it depends on the polarizer efficiency, the light collimation, the LCD efficiency, and others that I'm not yet aware of.
So where did u get this pj and why are u trying to diy it?