how did you polish that for a optical circuit? I have done it for cosmetic reasons by going through sand paper then going through automotive polishing compounds with many steps, and it looked good, but time consuming. However it was all salvage so it saves me money (150 to 3000 and 4 different compounds on around 20 substantially sized pieces (between 1.5x1.5 feet to 12x2 inches) !!!!). Oddly enough my shop vac caught on fire a month later.
fyi going through all the steps is very annoying and its worse to work with then wood IMO. If you work with plexiglass that is old and needs polishing, don't plan too many things at once that need to be refinished or it will be a painful experience. Non transparent plastics polish wonderfully though.
You might get better results if you invest in acrylic polishing compounds and abrasives, rather then using automotive stuff.... but its not an appealing investment for me at the moment.
This kit looks interesting
https://www.rockler.com/turning-finishing-kit?country=US&sid=V91040&promo=shopping&utm_source=google&utm_medium=cpc&utm_term=&utm_content=pla&utm_campaign=PL&tid=pla&gclid=CjwKCAjwn9v7BRBqEiwAbq1Ey32zt6NtWOlE_qfelMXMcjBqWZFJLoiIngtyv8l8Xp00H54q3IuWlBoCgiMQAvD_BwEI imagine combining that with the Novus compounds might be a good bet
I know that youtube guy that does all the cryogenic experiments is not happy with polishing plexiglass either (applied science)