Freeform lenses made by liquid polymers

Source: Technion – Israel Institute of Technology

An Interview with Dr. Valeri Frumkin

Researchers at Technion (Israel Institute of Technology) have developed an innovative method for producing high-quality optics using liquid polymers. The technology has several conceivable applications. It can potentially be used to produce spectacle lenses – from single vision to progressives – but also telescopes in future. The process was developed by Prof. Moran Bercovici and Dr. Valeri Frumkin. MAFO spoke with the latter about the potential of the new process. By Hanna Diewald

Dr . Valeri Frumkin.Source: Ms. Mas You were the person who first developed the method to produce freeform optical lenses with liquids. Can the technology actually be used to produce freeform lenses in future? Yes, we hope so. We are an academic lab and obviously still in the development process, all the demonstrations that have been presented in the papers are done manually.

How does your invention work exactly? Instead of using mechanical processing, the standard way of fabricating lenses today, we do not process anything. We define geometrical boundary constraints for something we call a “bounding frame” and then inject a liquid polymer into an immersion liquid. This liquid cancels gravity and gravitational effects, wherefore the polymer itself neither sinks nor flows to the surface – it just stays there. The shape of the polymer is determined by the shape of the bounding frame and the volume injected. The good thing is, the optical surfaces never get in contact with any mold or frame. There is no issue with removing them from walls or designing molds. We just get this perfectly smooth surface – with a surface roughness consistently of sub nanometer – without any effort.

What are the advantages of your technology? One advantage of this method – even if we just look at the simplest spherical and cylindrical surfaces – is the fact, that we can process it in seconds. Another advantage is that there is almost no infrastructure necessary – no heavy, expensive machinery, no pollution and nothing is going to waste. The only issue that we are currently working on is reproducibility. For example, if I want to create a specific type of lens and want to be able to make, let us say 50,000 of these lenses, this obviously requires automation.

Are there any limitations on the product side. For example, will you be able to produce progressive lenses? We showed in our paper that we can make freeform optics. We can produce a very smooth and infinite range of optical surfaces that can be quite complex but there is one important thing: we cannot create any optical surface! We can design and fabricate our own progressive lenses precisely, based on the functions given by the physics of liquid interfaces. In our opinion, the smartest way to progress is not to try to approximate designs of other optical engineers, but rather design our own lenses based on the needed functionality.

Are transparency and image quality comparable to those of conventional lenses? There are some aspects to this question. The optical quality in principle is comparable, in some cases even better. You will not be able to see a difference, as our eyes are very good at correcting various defects. If you measure the optical quality, you will see a difference. This difference comes down to the fact that this is an industry that already exists for hundreds of years, it is very developed, and we are just in our infancy. It will take a while to catch up. Furthermore, the quality depends on the material used. We can use anything that is liquid and can be solidified. It does not even have to be a polymer. If we use UV curable polymers or thermosetting polymers, each of them has their own challenges. UV curable polymers are extremely easy to polymerize as they polymerize very fast, but if the polymerization is not uniform, you can induce variations in refractive indexes or variations in the shapes. Another aspect is the shrinkage of polymers. Major shrinkage can cause deformations, which also affect the properties, but as we can work with a very wide range of polymers, we are searching for the best candidates. And you can use thermosetting polymers also, just mix them with a crosslinker. The polymerization will be perfect in the sense that it is always uniform. It really comes down to materials when speaking about optical quality.

Is the process also suitable for mass production in the future? In principle, there is no limitation but currently everything is done manually. However, a precise fabrication requires repeatability. The injection process must be automated and the specific frames need to be identical to one another. There are lots of small technical engineering issues. Those are small issues when you are a company but they are not so small when you are an academic lab, because everything requires a lot of work and there is a limited bandwidth in terms of time and people. It takes time to get to the point that we can consistently produce lenses, on the level that is required by the industry.

How long will it take to optimize your process for industrial production? It depends. There are some advantages of being in the academia and other advantages of starting a company and doing it on

Deployment of a liquid lens. Source: Technion – Israel Institute of Technology

Polymerization process. Source: Technion – Israel Institute of Technology

Mor Elgarisi presenting a huge lens. Source: Technion – Israel Institute of Technology

an industrial scale. The advantage of the latter is that you do not have anything else to do. You can hire engineers, developers, chemists, put everyone on the desk and that will be the fastest way to solve the problem, obviously. The good thing of being in academia is that we are just scientists. Everybody is very willing to collaborate and show us what they are doing. This is great because we are learning a lot and it allows us to improve the method significantly. If we were a company, nobody would let us walk through their factory.

F.l.t.r.: Omer Luria (lab engineer and leader of the NASA collaboration), Mor Elgarisi (PhD student currently leading this project at the lab), Prof. Moran Bercovici (head of the Fluidic Technologies laboratory at Technion). Source: Technion – Israel Institute of Technology

So at least for now, we are trying to leave it in the academia, until we feel that the method is mature enough and we understand all the technical difficulties. We are sure that there are many challenges we are not even aware of now.

Is this technology also applicable to the contact lens or IOL industry? In principle, yes – at least as far as we can tell. We can make very very large lenses for telescopes, for example, or very small ones – the physics is the same. However, the current technology used to make contact lenses seems to me to be very efficient. The question that arises here is: Does our technology have an advantage over the existing technology?

Do you already have a major target audience in mind? We do not know yet… The lowest hanging fruit is to create simple spherical-cylindrical corrections and you still save this entire array of machines. That would already be a major improvement for the industry and it is relatively easy to get to that stage. From there, we can build on that. We can start thinking about injecting directly into eyewear frames, so you do not need to cut the lens and you can think about doing progressive lenses. Very interesting for us are also freeform optics and rapid prototyping as many people in the industry told us that even if we do not produce a perfect lens but one that shows the functionality and allows them to test the design within minutes, it would be a very interesting direction. You can imagine having a device – equivalent to a 3D printer – and you enter a CAD file and design some plugins that connect our method to a bounding frame. The device creates the bounding frame, injects the polymer and you have the testing component. However, what actually started the idea of trying to create optics was a conversation with other scientists about a huge problem. There exists a major challenge in the developing world of having access to affordable eyewear. We found this report from the World Economic Forum that 2.5 billion people do not have access to eyewear. This is a huge problem for the economy and the people. You can send cheap glasses in a container to a country but this is not really a long-term solution. Instead, you need to provide the capabilities to produce on-site in good quality. Our method might be perfectly suited for that because you do not need a factory. This is something we are very interested in, in terms of doing something good.

Thank you for the interview. n

Liquid optics in space

The researchers also collaborate with NASA as the method relies on the fact that it eliminates gravity. In space, microgravity conditions can be achieved without using an immersion liquid and polymerization is unnecessary. This allows producing huge liquid mirrors using the same physics. The method will be much cheaper than whatever is done today, as it allows creating the optics in space instead of sending it there.