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Optics and photonics

Optics and photonics

Laser-lit photonic integrated circuits aim for a brighter future

20 Apr 2022 Tami Freeman
Taken from the 2022 Physics World Optics and Photonics Briefing, where it appeared under the headline "Inscribing the way to a brighter future".

VitreaLab, a photonics start-up based in Vienna, was the winner of this year’s SPIE Startup Challenge. Co-founder Jonas Zeuner talks to Tami Freeman about the company’s unique laser-lit chip technology and how it enables high-performance, power-efficient displays

Chiara Greganti and Jonas Zeuner, co-founders of VitreaLab
Photonics start-up Chiara Greganti and Jonas Zeuner co-founded VitreaLab in 2018. (Courtesy: VitreaLab)

VitreaLab is developing displays based on photonic integrated circuits; how are these created?

Essentially, we take a standard piece of display glass and we put it in our laser-writing system, which is composed of a femtosecond pulsed laser and a motion stage. Then we focus the laser on a specific 3D position inside the glass and locally melt the glass. This raises the index of refraction, and if you string along this modification, you create a light channel, or waveguide. As the index of refraction is higher in these waveguides, light undergoes total internal reflection and is guided in a similar way to inside an optical fibre. The waveguides have diameters of 2 or 3 µm and we use them to build very complex photonic networks. We can distribute the light from a single laser diode to tens of thousands, hundreds of thousands, or even millions of separate laser beams.

Is this the laser-lit chip?

The laser-lit chip is essentially the waveguide technology integrated with a nanoimprint layer on the glass surface, which reshapes the beams a little. But it is essentially a piece of glass that emits a very dense array of red, green and blue laser beams. The beams are so tightly spaced that you can actually slot this chip behind a standard liquid-crystal display (LCD) panel and deliver one laser beam per pixel. And since you can’t see the pixels in such a display, you can imagine how dense this beam array is. This technology can create a lot of new display types, in both 2D and 3D.

We can go from 5% transmission through the display stack to 90%: a huge jump in energy efficiency

What are benefits of using these laser-lit chips in displays?

Even after decades of development, the displays that we have today are fairly bad in many aspects. An LCD typically works by having a rectangular white light source such as an LED at the back of the screen and a filter array in front of it that subtracts light to create the image. But this is an incredibly wasteful process, you waste about 95% of the light being emitted. If you look at a laptop screen with a reasonable brightness, for example, you can imagine how incredibly bright the screen has to be at the back, and this drains the battery of your device tremendously. 

What we are doing is essentially just making the light flow much more easily through the entire liquid-crystal stack. It doesn’t get scattered, it doesn’t get colour filtered and it doesn’t create polarization-based loss. In this way, we can go from 5% transmission through the display stack to 90%. This makes a huge jump possible in energy efficiency. We see this as the strongest draw, what we can do for standard 2D display panels, this tremendous increase in energy efficiency. 

VitreaLab uses a unique laser-writing technology to inscribe tiny wave-guides into glass

VitreaLab is also planning to create the first full holographic display, how will this work?

Holography is an often misused physics term – not everything that is a 3D display is a hologram. Holographic displays, by definition, are something that are interference-based and laser-based. How a holographic display works is that you have to have a huge laser wavefront, something highly continuous, then you make tiny modulations, phase shifts, and from this you can create a complex wavefront that encapsulates your entire image. Typically, you would use a laboratory laser, widen the beam with a big lens and eventually let that impinge on your panel – but that’s not practical for consumer products. 

That’s where we come in: we miniaturize all of that. Our unique capability is to provide this wavefront, the laser light that you need to create a holographic image, in a form factor that nobody else can produce. We are able to control the laser light very well and enable this holographic back-light component. This will make consumer holographic displays possible.

Has VitreaLab released a commercial device yet? 

We are still in the early R&D stages, we have been developing this technology now for three years. We have shown, in our YouTube channel and also at the Photonics West conference, the first proof-of-concept chips, at 15 × 15 mm and 20 × 20 mm. We demonstrated colour images using our laser-lit chip and just an off-the-shelf LCD component. The cool thing we can already show is that you can produce colour images just using an LCD without colour filters, so essentially a monochrome display unit. But because we illuminate each sub-pixel with the correct colour with our separate beams, we can create colour images out of that.

What type of display are you targeting for your first products?

At the moment, we are targeting mobile- to laptop-size displays, maybe also up to monitor sizes for 3D displays, 25 or 28 inches, but definitely nothing larger than that for now. We did some testing, and it seems that when you use a laptop for web surfing, at least half of the energy is just going to the display. So if you can reduce this by 80 or 90%, of course it will make a tremendous difference to your run time. Something similar should also be true for smartphones.

Finally, why do you think VitreaLab won the SPIE Startup Challenge?

I hope that we were chosen because we delivered a good pitch and the jury members were happy with what we presented. We made a statement that we can fundamentally change what this displays space can do and bring it into a new era, into the laser era, and I think this really resonated with them. And, we have evidence that we can actually do this, with these proof-of-concept devices that we were showing during Photonics West. It’s a great boost for us because it’s a renowned award and it validates us with this display technology that’s very different to what everybody else does.

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