Technical Paper26

Journal of the HKPCA / 2018 / Autumn / Issue No. 69

Micro embossing Equipment for-Precision Optical Microstructures

A low-cost and energy-efficient technology

to make micro- and nano-lenses

[summary]

[main story]

Cameras used to be steeply priced beyond the reach of most

families. One reason was the high cost incurred in grinding and

polishing the lenses by hand. Nowadays, everyone can be a

photographer as all smartphones come with camera functions

and taking photos costs next to nothing. Camera lenses cost

less because they can now be moulded, thanks to

technological advancement. To bring the cost down further

while enhancing productivity and energy efficiency, researchers

from the Department of Industrial and Systems Engineering,

The Hong Kong Polytechnic University (PolyU), invented a

micro-embossing system that produces micro- and nano-

lenses at only two-thirds of the existing cost. It also saves over

90% electricity while shortening the production cycle.

Remember the time when a camera was a piece of expensive

equipment not affordable to every family? And if the lens was

Prof. Wing-bun Lee (2 from right), Dr Lihua Li (3 from right) and the research

team at PolyU

nd rd

The micro-embossing equipment

Institute for Entrepreneurship, The Hong Kong Polytechnic University

Technical Paper 27

www.hkpca.org

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 the 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, PolyU, 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.

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.

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 is 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

Conventional Glass Moulding

Innovative Glass Moulding

The mould (indicated by the blue arrow) and the glass (indicated by the green

arrow) during the embossing process

Technical Paper28

Journal of the HKPCA / 2018 / Autumn / Issue No. 69

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, Micro-embossing Equipment for Precision Optical

Microstructures won a gold medal in the 46th International

Exhibition of Inventions of Geneva, Switzerland.

The original article was published in the September 2018 issue of Technology

Frontier, an e-Newsletter of The Hong Kong Polytechnic University.

2018 9

The Micro-embossing Equipment for Precision Optical Microstructures won a

gold medal in the 46 International Exhibition of Inventions of Geneva.

46

th