Periodic Reporting for period 1 - BB-SLM (Polychromatic digital optics for structured light)
Période du rapport: 2020-03-01 au 2022-02-28
The scientific objective of this project is to develop a portable, efficient liquid crystal-based optical device to control the flow of polychromatic light using external electric and optical fields. The liquid crystal-based optical devices are well known and widely used in display technologies. We focus on cholesterics liquid crystals to efficiently control the spatial distribution of polychromatic light using computer-generated digital signals, and hence easily integrated into the existing optical technologies. It is worth noting that the current SLM technologies are designed to be monochromatic for maximum efficiency, so application is limited to a single wavelength of light. This two-year project is designed to develop a cutting-edge, digitally controlled spatial light modulator with maximum efficiency for a range of wavelengths. Such a device is anticipated by incorporating the achromatic nature of geometric phases with spin-dependent broadband circular Bragg-reflection from an electrically controlled cholesteric liquid crystal (ChLCs). ChLCs are chiral nematic liquid crystals. During this project, we aimed to find and demonstrate innovative solutions to fully control the spatial properties of ChLCs patterning towards the development of novel devices enabling efficient and polychromatic beam shaping. Subsequently, one can efficiently encode and decode light's all degrees of freedom; colour, polarisation and intensity in a telecommunication channel, pushing further the existing technological limitations for high-speed data manipulation and transfer and other photonic technology.
Conclusions of the action: -
Conventional ChLC and the cells are not suitable for the physical effects we were looking for, to realise the SLM proposed for the project. One should develop a new synthesising protocol to realise a new phase of ChLC whose supra-molecular structure alters axially at the boundary in response to the external electric field. Hence, we invited a research group from the USA who has strong expertise in synthesising unique kinds of LCs. They have developed and optimised a protocol to realise a unique ChLC cell with good homogeneity and sent us for the study. We have tested the samples and studied the phase modulation of the Bragg-reflected beam as a function of an external electric field. The preliminary studies have been completed and the results are promising for realising the anticipated device. Hence the host institutes will carry out the research and development activities, and the project will be completed in another year.
Website details: No specific website has been developed for the project. The researcher's website projects page link is given for the question
Conclusions of the action: -
Conventional ChLC and the cells are not suitable for the physical effects we were looking for, to realise the SLM proposed for the project. One should develop a new synthesising protocol to realise a new phase of ChLC whose supra-molecular structure alters axially at the boundary in response to the external electric field. Hence, we invited a research group from the USA who has strong expertise in synthesising unique kinds of LCs. They have developed and optimised a protocol to realise a unique ChLC cell with good homogeneity and sent us for the study. We have tested the samples and studied the phase modulation of the Bragg-reflected beam as a function of an external electric field. The preliminary studies have been completed and the results are promising for realising the anticipated device. Hence the host institutes will carry out the research and development activities, and the project will be completed in another year.
Website details: No specific website has been developed for the project. The researcher's website projects page link is given for the question
The researcher first studied different chemical combinations for the ChLC and the alignment layer to observe the re-orientation of the boundary orientation angle. ChLC with planar boundary condition (LC molecules close to the boundary are oriented parallel to the substrate) exhibit strong circular Bragg reflection normal to the substrate. However, our initial study shows that the planar-planar configuration is not adequate to observe the re-orientation of angle due to the strong surface orientational stiffness at the boundary. Consequently, the effect was investigated in hybrid cells (i.e. planar-homeotropic – LC molecules oriented perpendicular - boundary conditions) where the Bragg reflection is expected from the homeotropic side with the negligible stiffness. This option also failed to observe the anticipated effect as it lacks homogeneity in the order of laser beam scale (100s of microns).
Rigorous search in the rich ChLC literature leads us to open an international collaboration with a pioneer in preparing a unique phase of ChLC at Kent University, USA. The key advantage of this ChLC is that an external electric field can change its pitch through the winding/unwinding of the helical structure while preserving its structural periodicity. Hence, one can exploit this extraordinary behaviour to re-configure the orientation angle with the field under the proper boundary conditions. That is, winding or unwinding the helical structure should change the effective boundary orientation angle associated with the homeotropic cell.
Subsequently, a few samples of such ChLC are prepared at Kent university to re-initiate exploration for the BB-Pixel. Unfortunately, the homogeneity of the first generation samples was not adequate (<50microns) to test the anticipated geometric phase modulation of the Bragg reflected beam as a function of an electric field. After the first set of attempts, the second set of samples is prepared at Kent University with an improved protocol for achieving beam scale homogeneous liquid crystal and transferred to us for exploration. Also, we decided to use the liquid crystal in a hybrid boundary condition provides better inhomogeneity while not compromising the efficiency of Bragg reflection. Hence this designed and the realised sample is observed to be suitable for realising the targeted BB-pixel, the building block of the BB-SLM. Electrically controlled phase modulation of Bragg reflected light beam is subsequently observed. These results kick-start the development of a novel generation of optical phase modulation devices and generate both academic and industrial interest.
Overview of the results and their exploitation and dissemination: -
After developing and receiving the unique ChLC sample, we have carefully studied the electric field-induced phase modulation of the Bragg-reflected beam from the ChLC sample in an interferometer with reference to the incident beam. We observed at least three cycles of phase modulation for the reflected beam without changing its reflectance magnitude. Please note that a cycle of phase modulation is sufficient for the progress of the project. These results encourage us to invite additional collaboration with the expertise in electronics and micro-fabrications to realise the prototypic 5X5 pixel SLM. The results are obtained in the last months of the project duration, and the research and development activities will be continued at the host institutes. This will eventually allow us to disseminate the results to the public.
Rigorous search in the rich ChLC literature leads us to open an international collaboration with a pioneer in preparing a unique phase of ChLC at Kent University, USA. The key advantage of this ChLC is that an external electric field can change its pitch through the winding/unwinding of the helical structure while preserving its structural periodicity. Hence, one can exploit this extraordinary behaviour to re-configure the orientation angle with the field under the proper boundary conditions. That is, winding or unwinding the helical structure should change the effective boundary orientation angle associated with the homeotropic cell.
Subsequently, a few samples of such ChLC are prepared at Kent university to re-initiate exploration for the BB-Pixel. Unfortunately, the homogeneity of the first generation samples was not adequate (<50microns) to test the anticipated geometric phase modulation of the Bragg reflected beam as a function of an electric field. After the first set of attempts, the second set of samples is prepared at Kent University with an improved protocol for achieving beam scale homogeneous liquid crystal and transferred to us for exploration. Also, we decided to use the liquid crystal in a hybrid boundary condition provides better inhomogeneity while not compromising the efficiency of Bragg reflection. Hence this designed and the realised sample is observed to be suitable for realising the targeted BB-pixel, the building block of the BB-SLM. Electrically controlled phase modulation of Bragg reflected light beam is subsequently observed. These results kick-start the development of a novel generation of optical phase modulation devices and generate both academic and industrial interest.
Overview of the results and their exploitation and dissemination: -
After developing and receiving the unique ChLC sample, we have carefully studied the electric field-induced phase modulation of the Bragg-reflected beam from the ChLC sample in an interferometer with reference to the incident beam. We observed at least three cycles of phase modulation for the reflected beam without changing its reflectance magnitude. Please note that a cycle of phase modulation is sufficient for the progress of the project. These results encourage us to invite additional collaboration with the expertise in electronics and micro-fabrications to realise the prototypic 5X5 pixel SLM. The results are obtained in the last months of the project duration, and the research and development activities will be continued at the host institutes. This will eventually allow us to disseminate the results to the public.
The geometric phase was always a hot topic in physics, especially optics, due to its inherent achromatic nature. The achromatic nature of the anticipated digitally controlled phase modulating device will lead to the development of novel photonic technologies or improvisation of existing technologies by the maximum exploitation of most of the attributes of the light (Amplitude, spectral, spin and angular momenta). The simultaneous manipulations of the infinite-dimensional spectral degree of freedom of a photon along with its spatial and polarisation degrees of freedom will lead to the realisation of next-generation ultrafast information technology, where the use of ultra-short pulses having large bandwidth is necessarily used. Hence the project directly contributes to the European society's technological advancement through the invention of polychromatic digital optical elements and a kick start of a new class of optical beam modulators. At the same time, the researcher's academic leadership directly boosts the educational/research activities and scientific temper in his parental society back in India and elsewhere.