Microscopic glass blowing has been previously used to make microlenses, but it usually involves gas expansion from a single reservoir. Now researchers have developed an axicon fabrication method that combines gas expansion from multiple reservoirs to produce the optical component’s conical shape. The technique shapes the surface from underneath leaving a high-quality optical surface, unlike commonly used methods like etching transfer from a 3-D mask that engrave the wafer from above.
To carry out the new microscopic glass blowing method, the researchers deposited silicon cavities in concentric rings that were then sealed with glass under atmospheric pressure. Placing the silicon and glass stack in a furnace caused gas trapped in the cavities to expand, creating ring-shaped bubbles. These bubbles pushed out the glass surface to form cone shapes and then the opposite side was polished away to leave only the shaped lenses.
Although all the processes they used are standard for microfabrication, the researchers applied these techniques in non-standard ways to make miniature glass axicons. The technique could be applied to create other shapes, even ones without cylindrical symmetry.