Periodic Reporting for period 1 - Dynamo (Dynamic Spatio-Temporal Modulation of Light by Phononic Architectures)
Période du rapport: 2022-03-01 au 2023-02-28
Imaging technologies are ubiquitous, helping us monitoring our health, exploring our environment and in our telecommunications. At the heart of every optical imaging technology lies a component responsible for shaping the light beam in a spatial pattern according to an electrical or optical input. The incident light can be modulated in its phase, intensity, polarization, or direction, originated by various electro-optic or magneto-optic effects and by materials that modulate light by surface deformation. The most enduring, and continuously evolving, component in charge of this light modulation is the Spatial Light Modulator (SLM). The SLMs were originally developed for use as digital display screen technology, where large arrays of individual electronically addressable pixels must rapidly modulate light by some physical means to produce an image (an analogue is digital light projectors for feature films and presentations). Perhaps the most familiar example of this technology is the liquid crystal display (LCD), where electronic control of the liquid crystal orientation allows control of optical polarization, and, in combination with a polarizer, amplitude modulation of a backlight.
The major limitations in current imaging technologies are speed and resolution, and both impediments are originated by how the light is modulated in the device. Limitations in resolution have been overcome by several methods, some of them even deserving the Nobel prize, however the speed at which the spatial modulation of light is shaped remains limited by the refresh rate of current SLMs, which is of the order of 100kHz for the best of the devices. This is because SLMs and similar components operate sequentially, that is to say, they shape the light beam in different patterns but the time interval between patterns is limited by the refresh rate of the device. In Dynamo we will develop a breakthrough technology that will send all the possible patterns of the device simultaneously, and encoded in a short pulse of one nanosecond, creating the concept of parallel beam shaping or dynamic spatio-temporal light modulation device.
To give an idea of the magnitude of this breakthrough, we compare this improvement in the time to process images with the improvement in the clock frequency of computers: the first general purpose electronic computer, the ENIAC, had a clock frequency of 100kHz in 1945. It was not until 2000 where AMD reached the 1 GHz in their computers. Processing images is broadly similar to processing data in general, so this is indicative of a jump forwards of fifty years in the realm of imaging; the outcomes from this project offer to accelerate imaging technologies and place European science and industry at the forefront of the inventions and advances that will follow.
The major limitations in current imaging technologies are speed and resolution, and both impediments are originated by how the light is modulated in the device. Limitations in resolution have been overcome by several methods, some of them even deserving the Nobel prize, however the speed at which the spatial modulation of light is shaped remains limited by the refresh rate of current SLMs, which is of the order of 100kHz for the best of the devices. This is because SLMs and similar components operate sequentially, that is to say, they shape the light beam in different patterns but the time interval between patterns is limited by the refresh rate of the device. In Dynamo we will develop a breakthrough technology that will send all the possible patterns of the device simultaneously, and encoded in a short pulse of one nanosecond, creating the concept of parallel beam shaping or dynamic spatio-temporal light modulation device.
To give an idea of the magnitude of this breakthrough, we compare this improvement in the time to process images with the improvement in the clock frequency of computers: the first general purpose electronic computer, the ENIAC, had a clock frequency of 100kHz in 1945. It was not until 2000 where AMD reached the 1 GHz in their computers. Processing images is broadly similar to processing data in general, so this is indicative of a jump forwards of fifty years in the realm of imaging; the outcomes from this project offer to accelerate imaging technologies and place European science and industry at the forefront of the inventions and advances that will follow.
During the first year of the Dynamo project, the following tasks have been developed:
1- Formulation of the theoretical aspects of the new imaging concept we are introducing
The aim of Dynamo is the development of time-modulated phononic surface which will modify the spatio-temporal profile of the optical wavefront. During the first year of the project, we have shown that this modulation of the optical field can be used for super resolution and single-pixel imaging. We have also shown that the theory of compressive sensing can be applied, reducing the number of measurements needed to perform the reconstruction of the image [1].
2- Development efficient algorithms for the calculation of localized modes in engineered phononic surfaces
During the first year of the project, we have explored several methods to efficiently reduce this computation time, since during the project we will need to study several structures and even design the optimal ones, which can be impossible with current algorithms. Although the so called “multiple scattering theory” continues being our first option [2], we have explored three other possibilities: (a) Guided mode expansion method, (b) Mode matching theory, (c) Dispersion relations of quasi-periodic materials.
3- Development of a picosecond ultrasonics setup
The experimental part of the project takes place in two institutions, the Sorbone University (France) and the University Jaume I (Spain). In the former, where the picosecond ultrasonics setup is already running, we will characterize the samples, while in the latter these samples will be used to develop single-pixel imaging applications. It is here where the picoseconds ultrasonic setup has to be built from the beginning and it has been the main task during the first year of the project.
4- Fabrication and characterization of phononic surfaces with ordered and quasi-periodic patterns for calibration of the setup
Several samples have been fabricated at CSIC. We are using different materias and architectures to explore the best configuration for the aim of the project. A promising combination found so far is the thin-soft layer atop a rigid substrate, since this system presents a strong confinement on the thin layer due to the cut-off frequency characteristic of the hard-soft boundary, resulting in localized resonances that can be coupled tunning the thickness of the layer. Picosecond ultrasonics experiments have been done at Sorbone University to study the samples.
[1] Packo, P., & Torrent, D. (2022). Far-Field Perfect Imaging with Time-Modulated Gratings. Physical Review Applied, 17(6), 064040.
[2] Martí-Sabaté, M., Guenneau, S., & Torrent, D. (2022). High-quality resonances in quasi-periodic clusters of scatterers for flexural waves. AIP Advances, 12(8), 085303.
1- Formulation of the theoretical aspects of the new imaging concept we are introducing
The aim of Dynamo is the development of time-modulated phononic surface which will modify the spatio-temporal profile of the optical wavefront. During the first year of the project, we have shown that this modulation of the optical field can be used for super resolution and single-pixel imaging. We have also shown that the theory of compressive sensing can be applied, reducing the number of measurements needed to perform the reconstruction of the image [1].
2- Development efficient algorithms for the calculation of localized modes in engineered phononic surfaces
During the first year of the project, we have explored several methods to efficiently reduce this computation time, since during the project we will need to study several structures and even design the optimal ones, which can be impossible with current algorithms. Although the so called “multiple scattering theory” continues being our first option [2], we have explored three other possibilities: (a) Guided mode expansion method, (b) Mode matching theory, (c) Dispersion relations of quasi-periodic materials.
3- Development of a picosecond ultrasonics setup
The experimental part of the project takes place in two institutions, the Sorbone University (France) and the University Jaume I (Spain). In the former, where the picosecond ultrasonics setup is already running, we will characterize the samples, while in the latter these samples will be used to develop single-pixel imaging applications. It is here where the picoseconds ultrasonic setup has to be built from the beginning and it has been the main task during the first year of the project.
4- Fabrication and characterization of phononic surfaces with ordered and quasi-periodic patterns for calibration of the setup
Several samples have been fabricated at CSIC. We are using different materias and architectures to explore the best configuration for the aim of the project. A promising combination found so far is the thin-soft layer atop a rigid substrate, since this system presents a strong confinement on the thin layer due to the cut-off frequency characteristic of the hard-soft boundary, resulting in localized resonances that can be coupled tunning the thickness of the layer. Picosecond ultrasonics experiments have been done at Sorbone University to study the samples.
[1] Packo, P., & Torrent, D. (2022). Far-Field Perfect Imaging with Time-Modulated Gratings. Physical Review Applied, 17(6), 064040.
[2] Martí-Sabaté, M., Guenneau, S., & Torrent, D. (2022). High-quality resonances in quasi-periodic clusters of scatterers for flexural waves. AIP Advances, 12(8), 085303.
So far the results achieved have arleady demonstrated the possibility to:
1- Perform single detector imaging with time-modulated surfaces.
2- Designing of bound states in the continuum for SAWs.
3- Ultrafast calculation of resonant modes of randomly placed elastic resonators.
4- Fabrication of large area moiré patterns for SAWs
[1] Mendoza‐Carreño, J., Molet, P., Otero‐Martínez, C., Alonso, M. I., Polavarapu, L., & Mihi, A. (2023). Nanoimprinted 2D‐chiral Perovskite Nanocrystal Metasurfaces for Circularly Polarized Photoluminescence. Advanced Materials, 2210477.
[2] Marc Martí-Sabaté, Bahram Djafari-Rouhani, and Dani Torrent. (2023). Bound states in the continuum in circular clusters of scatterers. Phys. Rev. Research 5, 013131
1- Perform single detector imaging with time-modulated surfaces.
2- Designing of bound states in the continuum for SAWs.
3- Ultrafast calculation of resonant modes of randomly placed elastic resonators.
4- Fabrication of large area moiré patterns for SAWs
[1] Mendoza‐Carreño, J., Molet, P., Otero‐Martínez, C., Alonso, M. I., Polavarapu, L., & Mihi, A. (2023). Nanoimprinted 2D‐chiral Perovskite Nanocrystal Metasurfaces for Circularly Polarized Photoluminescence. Advanced Materials, 2210477.
[2] Marc Martí-Sabaté, Bahram Djafari-Rouhani, and Dani Torrent. (2023). Bound states in the continuum in circular clusters of scatterers. Phys. Rev. Research 5, 013131