future view

Optics 2.0: the future of freeform optics

1 December 2017 • 5 min reading time

Freeform optics is a trend in optics in which systems become smaller and more compact, while their performance is maintained or even enhanced. TNO can both manufacture high-quality lenses and mirrors and build them into optical equipment: a unique combination. On Thursday 30 November, a symposium entitled ‘A Freeform Optics Future' was held, in recognition of this capability and to mark the arrival of three new machines.

Optics Manufacturing, the beating heart of Dutch Optics Centre, fabricates components for optical systems (including optical measuring systems). “Our specialist lenses and mirrors are used in all kinds of applications, from hospital equipment to communications devices. While it takes a great deal of experience to manufacture these high-quality components, we also require precision machinery. We recently purchased three new machines that will enable us to manufacture these components to an even greater level of accuracy. Our goal is to develop innovative optical instruments and associated systems, together with industry and other knowledge institutions. This new equipment is a real step forward in that regard.” explains Jantine Slinger, a project manager at TNO Optics.

Freeform optics

Freeform optics is a technique that is used in the development of high-quality optical systems. Conventional lenses and mirrors have a simple shape, either convex or concave, and they have their limitations. They cannot produce certain light-beam paths, so lenses and mirrors with a more complex aspherical or freeform surface (for example, a lens shaped like a banana or a saddle) are needed.

“Situations that previously required several lenses now only require one (or a few) special freeform lens”

This method can also be used to develop smaller, lighter, high-resolution lenses and mirrors. New systems containing these components can be made smaller and lighter, which is a big plus for aerospace instruments, for example. Due to their unusual shapes, however, it is more difficult to manufacture, test and measure such lenses and mirrors. This is where the three new machines (a measuring machine, a grinding machine and a polishing machine) come in. TNO has been producing freeforms for more than ten years, but the new machines provide a much wider range of options. They will make it possible to manufacture and test freeforms with greater accuracy than ever before.

Helping our customers to get ahead

“At Optics Manufacturing, we make specific components (lenses and mirrors) which are then incorporated into innovative systems to create unique, new products”, emphasizes Merijn Voets, a business developer at Optics Manufacturing. “We have specific in-house expertise in the field of optics. These skills, together with the right equipment, enable us to develop special, complex and accurate instruments capable of operating under extreme conditions. Few companies or knowledge institutes can match this. We can also advise clients on issues such as manufacturability and product costs. We use our expertise to help others get ahead.”

“TNO’s advice and products are used in the aerospace industry – for customers such as NASA, ESA and Airbus – and in various other sectors”

For instance, our advice and products are used in the aerospace industry – for customers such as NASA, ESA and Airbus – and in various other sectors. One specific example is TROPOMI. Mounted on the recently launched Sentinal-5P satellite, this instrument monitors air quality and the distribution of greenhouse gases. TROPOMI is based on a freeform telescope.

Unique products

Mirrors and lenses are also used in hospital equipment, lithographic equipment and communications equipment. “For instance, we are cooperating with the Dutch Kidney Foundation on the development of a new dialysis machine that kidney patients can use at home. This handy portable artificial kidney is small enough to fit on the bedside table at home. Conventional dialysis equipment requires 100 litres of dialysis fluid, but this portable device only needs a couple of litres. This is because the fluid can now be reused, thanks to an innovative sensor that monitors its ion concentrations. The only way to make a sensor like this is through the use of freeform optics”, says Bart Snijders, an Optics business consultant. Another example is the development of a new kind of microscope for medical research. A two-mirror freeform mirror system has made it possible to develop a compact microscope that is not only cheaper than current models but which also produces even sharper images.

“For instance, we are cooperating with the Dutch Kidney Foundation on the development of a new dialysis machine that kidney patients can use at home”

A new form of Wi-Fi

Optical components may also contribute to a new form of Wi-Fi. Mr Snijders explains that “The telecom sector currently makes connections using radio waves, but we are now nearing the limits of this technology’s capacity. New approaches are needed, and one option involves the use of light. Lasers can be used to send light beams from ground stations to satellites, and from one satellite to another. This requires transmitters and receivers that are compact and very precise. Freeform optics is key to the manufacture of such devices. Laser communication can also help us meet our growing need for data traffic in the future. Actually, in all of these applications, functions that previously required several lenses now only require one (or a few) special freeform lens.”

Accurate machines

All this is possible thanks to the three new machines that TNO has recently been able to acquire; a grinding machine, a polishing machine and a measurement machine. The great thing about the new grinding machine (a Cranfield Precision TTG 350) is that, in addition to convex, concave and flat shapes, it can also make freeforms. Uniquely, the machine has two vertical rotary axes, instead of the usual three-axis system (x,y,z). This enables it to grind with far greater accuracy.

The polishing machine (a Q-flex 300) can be used to polish ceramic and glass lenses and mirrors. Light is used to measure the roughness of a surface. The machine then uses computer algorithms to correct the surface as required, to a very high degree of accuracy. Polishing involves the use of cerium oxide or diamond (fluid), in a technique known as magnetorheological finishing (MRF).

Optical components are measured before, during and after production and finishing, to check that they meet the specifications. The ZEISS PRISMO ultra can measure freeforms to a high degree of accuracy. This new CMM (Coordinate Measurement Machine) is a fully automated measuring machine. It uses a probe to measure the manufactured components after they leave the workshop, and it checks them again once grinding has been completed. These three new machines will enable TNO to set itself apart from the rest even more effectively.

“The official commissioning of our machines took place at 30 November. During the event, we demonstrated some of this new equipment’s exceptional capabilities to everyone present”, Mr Voets concludes.


This TNO project supports the following Sustainable Development Goals

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