Remember the time when a camera was a piece of expensive equipment not affordable to every family? And if the lens was an “aspherical” one, a hefty price tag could be guaranteed. An aspherical lens has a freeform configuration instead of a concentric circular contour and it produces less aberration and sharper images than its spherical counterparts. In the old days, while spherical lenses can be mass-produced by machines, every piece of aspherical glass in a camera has to be ground and polished by hand. Fast forward to here and now, the ubiquity of smartphones has hugely democratized photography and everyone can take pictures at relatively low cost. One way to bring the cost down significantly is to use moulded lenses instead of ground and polished ones. To bring the cost down further, save energy and enhance productivity, Dr Lihua Li, Department of Industrial and Systems Engineering, led a research team to develop an energy-efficient micro-embossing technology to mould optical glass into high-precision aspherical micro- or nano-lenses at unprecedented low cost.
Conventional Glass Moulding
Glass optical components, including micro-nano optical elements with micron-sized glass microstructures, are much more difficult to mould than their plastic counterparts as glass requires a much higher temperature to soften. The whole process chamber is heated up using infrared heater and that consumes a lot of energy. Furthermore, as the moulds have to be able to resist corrosion and withstand high temperature and pressure, tungsten carbide is usually the material of choice. However, tungsten carbide is expensive, very stiff and difficult to mill with accuracy. The production cycle is long and costly, adding to the price tag of the end products.
Innovative Glass Moulding
That’s why the team came up with the novel micro-embossing concept. “Instead of heating up the whole glass moulding chamber, we only aim at locally heating up the surfaces. That means less time and less energy are required for preheating, moulding and cooling, shortening the production cycle,” Dr Li explained. To heat up the mould surface quickly, the micro-embossing system uses silicon mould inserts with a graphene-like carbon coating on the moulding surface. When electricity is applied, the coating heats up very quickly and the heat is retained in the silicon mould. It takes less than 2 minutes to heat up, press on and then cool the glass. Because of the unique properties of the silicon material, the mould itself also serves as a temperature sensing device, making rapid thermal control possible. In addition, silicon is far easier to shape than tungsten carbide, making this process more accessible commercially. Coupling with graphene-like coating and temperature control, the system provides an all-in-one design, encompassing moulding, heating and sensing at the same time. The team found that the micro-embossing system is much more energy-efficient, saving over 90% electricity than conventional glass moulding method, while reducing manufacturing cost to two-thirds of existing cost.
“Apart from smartphone camera lenses, the micro-embossing technology also make lenses for digital projectors, photocopiers, solar cells and 3D light field cameras,” Dr Li added.
In April 2018, the Micro-embossing Equipment for Precision Optical Microstructures won a gold medal in the 46th International Exhibition of Inventions of Geneva, Switzerland.
