I'm dismantling a few old DVD writers for parts and I'm curious about the specs on those parts I'm pulling out carefully. One of the pieces of glass appears to be a thin film dielectric filter/splitter. It's possible it is just a splitter used in the astigmatic/quad detector system for focusing... but because this is a writable system I'm wondering if it may also double as a bandpass/bandstop filter, as well. (A separate wavelength, memory serving, is used to hit a differently dyed polymer layer in the disk for writing than for erasing.) So I'm wondering if anyone already knows, roughly, the details of the thin film dielectric filter/splitter glass used in writable DVD units -- what it actually is.
I've looked around with google and found some things to read -- but all of it dated back at 1997 and earlier. Old. And no details on these parts that I could find today. (A lot of what I found is Japanese and Korean, which is expected, but of far less help to me.)
I may need to set up a cheap one-off spectrophotometer, callibrated with a merc-argon lamp, and do my own work in answering these questions. But it would certainly help if someone had some of the details in mind about these pieces of glass, before I try and set something up here.
Thanks in advance, Jon