Optical Ray-tracing software - not like povray!

[Neil Pilgrim <debian-science@kepier.clara.net>]

Hi,

As part of an Optics course I'm teaching, we use an old 'ray tracing' 
program which is used for modelling and learning geometrical optics in 
2D. However, it is commercial and out of date, so for next year we are 
hoping to use an alternative.

Does anyone know some kind of equivalent software, ideally open-source? 
Its very difficult to search for such software, since 'ray tracing' gets 
lost in a maze of pov-ray type software, all alike...

Thanks for any ideas,

--
Neil Pilgrim