Edible Optics

What materials can be used to make optical elements – that are transparent and mostly homogeneous -- but which are also edible? Think of this as an exercise in optical engineering with a very odd requirement. Optical designers are often bound by restrictions that require their materials to be transparent in certain regions of the spectrum, or are vacuum-qualified for use in space, or which must function at extreme ntemperatures. This is just a very different requirement. If it seems too outrageous, consider that there can be practical reasons for this requirement. Several edible optical devices have, in fact, already been designed and constructed.