A special type of thick biconvex optical lens is a Ball lens that usually has a sphere geometric shape. These are made of a single material such as BK7 or other optical glass/Fused Silica/CaF2 which is a commonly used material for ball lenses.
The smallest lens we produced is < 0.5 mm. We can process ball lenses using all types of glass material. Our price for PV industry may be as low as USD0.02/pcs. We are developing CSD-based AR-coating to provide a low-cost PV-coating solution.