Dichroic mirrors and filters are particularly effective for this kind of application (my first exposure to these were the mirrors for my homebrew HeNe gas lasers in high school, except that these particular mirrors reflected red (632.816 nm, especially) and transmitted blue).
Also check out dielectric mirrors. These are more broadband versions of the above. Distributed Bragg Reflectors are another sort of color-selective mirror that may be a fit considering that your application is to an optical fiber. Another name for this is a Bragg Grating.
"Low-cost" is subjective. Are we talking about quantities of one? One million? Is this a one-off sort of application or do you plan to mass-produce it?
Must it be plastic, as you say? Why? If your concern is optical coupling, say, there are ways to effectively couple materials having different IoRs.
Yes looking for low cost to be used in a consumer application if possible.Mass produced eventually.
But something in plastic would make it a compatible design with the POF i want to use,although other materials as you metioned are OK
I can use a beam splitter from Mitsubishi but would probably need two parts and this would be about $50 each in small quantities.
Was looking for a smaller footprint for the intended product and a little less cost for the consumer market for this applcation.Thgus beam splitter would be a physical constaring problem for this market
Otherwise will do for a special saftey product with higher costs justified.