Scientists working on the DYNAMO Project, fourth from the right: Dr hab. (Eng.) Paweł Paćko, Associate Professor at the AGH UST; photo: DYNAMO Project materials
Spatial light modulators (SLMs), used, for example, in optical imaging systems, from ordinary projectors to advanced biomedical technologies, could operate much faster if not for the limitations of the material from which they are made. The AGH UST scholars, within the international DYNAMO Project, want to design a new type of modulators using flexible metamaterials that would increase the modulation frequency by a million.
When we want to generate dynamic images, we need to change the parameters of the light beam that creates them repeatedly and quickly. The same goes for illuminating an object to project its image on the basis of the light reflected therein. To achieve this, the devices that we use to display and capture images are equipped with spatial light modulators (SLMs) that provide a passing light beam with the desired phase, intensity, polarisation, and direction. To serve this purpose, most SLMs use liquid crystals, the particles of which, after being activated by a mechanical pulse, assume a desired spatial pattern, creating a diffraction grating.
Modulators have reached their maximum spatial resolution confined by the laws of physics (the so-called ‘diffraction limit’), but their temporal resolution still remains several orders of magnitude below the limit dictated by the maximum optical frequency. Putting this into practice – improving the second parameter, it would allow us to display the images even more smoothly, and give us a chance to observe the changes in the shape or placement of the objects under scrutiny in time with an unprecedented precision.
The obstacle is the response time for the excitement of structures, which in modulators comprise a unit that gives the light beam the desired form. Liquid crystal models can generate up to 10,000 patterns per second, and specialised systems based on micromirror arrays – several times more. Current technology allows us to emit excitation pulses with gigahertz frequency, that is, thousands of times more than even the fastest SLM systems in use today.
The scientists working at the interdisciplinary DYNAMO Project, which is a consortium of several European research centres, including the AGH University of Science and Technology, propose a complete shift in the thought paradigm of light modulator frequency. The scholars have been devising a system that will allow them to encode many patterns within a single pulse. To this end, they want to design a metamaterial that will possess the properties of a periodic arrangement and change form depending on the imposed vibrational frequency with a varied spatial configuration.
‘A pulse is a signal that, within mathematical limits, allows us to excite all frequencies. Practically, this means an extremely wide applicational scope, which can be used in analyses. Therefore, by designing the crystal in a way to respond with various patterns shortly after such an excitement pulse has been emitted, we are able to considerably compact the information in time. In comparison to traditional light modulators that require mechanical frequency adjustment, in this case, everything will happen automatically as a result of the deformation of the entire system‘, explains Dr hab. (Eng.) Paweł Paćko, Associate Professor at the AGH UST Faculty of Mechanical Engineering and Robotics.
The AGH University of Science and Technology, together with the Universitat Jaume I in Castelló and Imperial College London, is responsible for delivering theoretical guidelines crucial for the production of such a metamaterial. ‘Usually, within a small frequency range, the vibrational modes are not that varied. Our goal is to compress a lot of such vibrational modes in a narrow frequency band, so that, with minimal shift in imposition, the deformation of the mirror is drastically different‘, clarifies Prof. Paćko.
The scholar also describes a possible appearance and operation mode of such a structure: ‘In general, we can imagine this crystal as a vibrating plate, which will be equipped with the so-called ‘spot lights’, for instance, small masses on springs. If we place such a mass on a spring on this plate, it will cause wave diffraction, which, in consequence, will change the vibrational mode of the entire system. If we place two of them, they will influence each other and, as a result, the wave field will be subject to multiple diffraction patterns.‘
‘Our idea is, firstly, to understand what is happening on a small scale, when there are few elements that interact with each other, and then to use this knowledge to design larger structures‘, adds the AGH UST scientist.
The production of a material with the aforementioned properties is a job for engineers from the Institut de Ciència de Materials in Barcelona, who specialise in creating nanostructures. The models they designed will be examined by scholars dealing with optoacoustics from the Institut des NanoSciences in Paris. The task of testing their application potential in imaging systems will be left to experts from Castelló. The last centre coordinates the entire project. The scientists hope to be able to present a solution that will allow them to increase the speed of light modulators even a million times.
‘There are a myriad of phenomena that occur on a small scale in time, which we are currently unable to capture images of. The initial inspiration for these investigations was soft tissue imaging; however, the application potential of the solution is wide, for example, in physics or metallography. In recent years, due to advances in electronics, we’ve seen considerable interest in how materials deform in a short time as a result of various events‘, says Prof. Paćko, listing potential applications for the new technology.
The project titled Dynamic spatial light modulators based on phononic architectures – DYNAMO received funding from the EU HORIZON-EIC-2021-PATHFINDEROPEN programme within Horizon Europe.