The demand for holographic optical elements (HOEs) is continuously increasing due to their potential applications in a wide range of quickly advancing technologies. The main challenge for HOE development is in the design and preparation of holographic materials, which satisfy environmental requirements during device exploitation. Photosensitive glasses are potential candidates for the development of HOEs with improved environmental stability, mechanical stability and hardness. Recently, a novel photopolymerisable hybrid sol-gel (PHSG) for holographic recording of volume gratings with high performance has been reported. Due to its valuable combination of properties, PHSG has potential for mass-production of highly efficient and durable optical devices with long-term stable performance at different ambient conditions. Nevertheless, the mechanism of grating formation is not fully characterised and understood. To achieve control over the performance of the material and further improve its properties, systematic study is required. In this research, the mechanism of grating formation in the PHSG is investigated by analysing two main effects contributing to the refractive index modulation. The first effect is density change due to both polymerization of monomers under holographic patterning and polycondensation caused by natural aging of the sol-gel material. The second effect is diffusion of mobile species such as dye molecules induced by concentration gradients and/or distribution of small nanoparticles caused by spatially varying heat dissipation resulting from light absorption during holographic patterning. Experimental results confirn that the mechanism of grating formation in the PHSG can be defined as the creation of spatially-varying refractive index within the bulk of the material mainly due to changes in density induced by photopolymerisation and polycondensation. Diffusion processes are observed to have low impact on the grating formation. The proposed model facilitates controlled and predictable diffraction efficiency of gratings recorded on the PHSG, thereby furthering the prospect of the development of HOEs with customisable specification.

Holographic solar concentrators stand to benefit from the low angular selectivity and high diffraction efficiency that comes with thin layers and a high refractive index modulation (RIM); as lower angular selectivity reduces the need for solar tracking. While RIM is significant in the development of effective solar concentrating devices there are other important properties like material chemical stability, physical robustness and sensitivity to atmospheric conditions that must be considered. Recent developments have put forward a photosensitive sol gel glass material that meets the criteria of physical and chemical stability with low sensitivity to its environment and reported RIM of 0.003. In this investigation the RIM of a robust photopolymerisable sol-gel glass with a high dynamic range and fast curing times is improved using a thermal post processing method during a post exposure diffraction efficiency growth process. This process was done to maximise the achievable refractive index modulation, and so, many optimisations including exposure time, wavelength, and post processing temperature were made. This was done for different holograms recorded at many different spatial frequencies (400 – 1000 l/mm) and thicknesses. Improvements of 200% to the RIM were observed in some holograms after thermal post processing compared to holograms that were not treated. The max RIM values achieved using this method was 0.0055. Bragg curves were modelled based on the highest achievable RIM in order to determine the minimum thickness value that would provide close to 100% diffraction efficiency while minimising angular selectivity. These holograms were then recorded to showcase the materials’ potential as a solar concentrator.

The study of the optical properties and behaviour of holograms stored in hydrogel matrices when the material is immersed in liquid medium represent a very important challenge currently. Hydrogels are 3D polymer networks capable of undergoing reversible volume changes. These hydrogels can be chemically modified to obtain materials with different properties such as to be sensitive to a range of relevant analytes. Emergent applications require that the holograms stored in hydrogels be time-stable in a liquid medium. One of the most important applications of this type of system are holographic sensors. Holographic sensors have advantages over other types of sensors such as the possibility of miniaturization due to the use of holographic techniques, the ability to produce three-dimensional images, real-time quantification, possibility of low-cost mass manufacturing and label-free analyte- responsive. Due to these advantages, these sensors have great potential to be used in different areas such as environmental detection, veterinary testing, pharmaceutical bioassays and medical diagnosis. Therefore, the optical behaviour of the holograms and the optimization of the hydrogel’s matrices must be well studied. When volume phase holograms are stored in hydrogels matrices in liquid medium, the holographic planes can undergo a bending process that give rise to asymmetries in the lateral lobes around the Bragg angle. This bending affect to the diffraction efficiency, wavelength of maximum diffraction efficiency and the angular sensibility. These parameters are used as signal transducers in holographic sensors in transmission mode. The general aim of this work has been study the bending that is produced in the holographic planes when unslanted transmission volume phase holographic grating with a frequency of 1200 lines/mm have been stored in hydrogel matrices based on acrylamide (AA) and N,N'-methylenebisacrylamide (MBA) using different solvents (dimethyl sulfoxide, water and buffer solution) during the manufacturing process. Considering previous works on bending, and grating attenuated hologram.

The geometry of refraction and interference of two plane laser beams into a flat recording package is sufficiently simple that analytic expressions can be derived for the beam and sample angles to write a given transmission or reflection hologram. The accessible range of grating vectors is constrained only by the coherent transfer function determined from the cut-off angle of writing ray vectors. To reach a larger portion of the grating space, as is typically required for materials testing and applications such as augmented reality waveguide couplers, one must add prisms to one or both sides of the sample. The constraints on possible grating vectors in this case are a complex interplay of the cut-off angle, the clear aperture of the prism faces, hologram position in the sample, and the limits of the motion system that positions the recording medium and writing beams. Further, the number of possible writing geometries jumps from two in the planar case (that is, reflection and transmission) to the square of the number of entry facets or 16 in the case of triangular prisms on both sides of the sample. Determining the best prism, writing beam, and stage configuration to write a required set of gratings at a multiplicity of locations in the sample thus becomes analytically intractable. We present a graphical method of solving this inverse problem. The foundation is a highly parallel, non-sequential ray tracer that solves for all possible holographic gratings given a specific sample geometry consisting of a film, substrates, and triangular prisms on one or both sides. The tool graphically presents the allowable grating vectors as a function of writing beams entering surfaces in all possible combinations, hologram position in the sample, and motion control such as writing beam and sample rotation and translation. Constraint regions due to the cut-off angle, surface clear apertures, and stage motion are illustrated to guide design modifications that would reach different regions of grating space. Finally, we show how this supports writing into curved films.

The current surge of interest in holographic photopolymers is motivated by display applications that often call for holograms in reflection geometry. However, the geometry of reflection holograms is uniquely sensitive to problems that arise from non-instantaneous recording, including volume shrinkage and off-target index development during exposure. Here we leverage a high-powered recording laser to compare holograms of varying writing power and exposure time pairings (with a consistent exposure intensity), showing improved hologram quality with shorter (higher-powered) exposures. Shorter, higher-powered reflection hologram exposures result in lower haze and higher diffraction efficiency.

The transition from exploring holographic photopolymer dynamics to designing a holographic display presents several challenges, including the need to create phase-matched holograms over large areas using high-intensity exposure conditions. High-intensity recording conditions result in low haze and highly diffraction efficient holograms, but such exposures are typically limited to a relatively low writing area. Here we demonstrate a method by which a high-intensity writing beam is rastered across a large region of holographic material in a manner which locks the phase of the hologram grating vector across the entirety of the exposed region.

Improving the photon collection efficiency in light-sensitive devices is crucial for next-generation photodetectors and solar cells. A valid strategy consists of placing a microlens or microlens array (MLA) on top of the active area of these devices, with sustained gains of up to 50% in their quantum efficiency. However, current technologies for micro-optics fabrication can be limited in throughput, attainable geometries, fill-factor (FF), or range of suitable substrates. In this talk, I will show how the combination of additive manufacturing with photopolymer materials can help fill this void and produce customized microlenses and MLA over planar, curved, and flexible substrates. Specifically, I will focus on two different strategies. The first one uses laser pulses to print liquid pre-polymer droplets on targeted locations of a substrate [1,2]. After a UV-curing step, the droplets become solid microlenses that exhibit almost perfectly smoothness. In the second strategy, termed laser catapulting (LCP), irradiation of a cross-linked photopolymer film results in the delamination and ejection of microdisks that are collected on a substrate of interest [3]. Following a thermal reflow process, the discs are converted into high-quality microlenses whose focusing power and geometry depend on the initial laser parameters [4,5]. I will present an in-depth experimental characterization of the two strategies, discuss their advantages and pitfalls, and illustrate their suitability in several applications, including enhancing the performance of single-photon avalanche diode (SPAD) arrays for super-resolution microscopy. 1. C. Florian, S. Piazza, A. Diaspro, P. Serra, and M. Duocastella, "Direct Laser Printing of Tailored Polymeric Microlenses," ACS Appl. Mater. Interfaces 8, 17028–17032 (2016). 2. S. Surdo, A. Diaspro, and M. Duocastella, "Microlens fabrication by replica molding of frozen laser-printed droplets," Appl. Surf. Sci. 418, (2017). 3. S. Surdo, R. Carzino, A. Diaspro, and M. Duocastella, "Single-Shot Laser Additive Manufacturing of High Fill-Factor Microlens Arrays," Adv. Opt. Mater. 6, 1701190 (2018). 4. S. Surdo, A. Diaspro, and M. Duocastella, "Geometry-controllable micro-optics with laser catapulting," Opt. Mater. Express 9, (2019). 5. S. Surdo, A. Diaspro, and M. Duocastella, "Printability conditions for an all-solid-state laser transfer," Appl. Surf. Sci. 506, (2020).

In this paper we investigate the use of photopolymer material as the sensor medium. This research will focus on the creation of self-written waveguides with the photopolymer and the interaction with the environment. This SWW can be used to measure direction of propagation and angle of incidence upon the polymer material. Under environmental force new SWWs can be measured and recorded within the PVA/AA on a 3D plane. These newly created SWWs, from numerical modelling, can represent the interaction with the surrounding environment. This can be used to measure force and direction of movement.

Holographic gratings that have been created through the exposing of a specific light beam upon a photosensitive polymer material have been known to also produce self-written waveguides (SWW). We will investigate the SWW and its ability to propagate an optical beam along its path. The reproduction of images processed as information within an optical beam and propagated along the SWW will be tested. The image will be analysed for coherence and clarity. The effect of Birefringence upon the information or image and its optical characteristics will be interrogated measured. The probably of information distortion and the presence will be studied and analysed through research, experimentation and numerical modelling.

In this letter, we employ vector wave polarization holography theory based on the dielectric tensor description. Newly developed vector wave polarized holography theory breaks up the limitation of paraxial approximation in polarization holograms. Various interesting phenomena have been investigated, the faithful reconstruction is of particular significance. The faithful reconstruction (FR) effect indicates that the polarization state of the reconstruction wave is identical to that of the signal wave, it can be achieved process when the intensity and polarization holographic grating attained a balance during after exposure. The FR property related to the linearly, circularly and elliptically polarization is investigated in our previous work. In our experiment, the recording medium we use is the bulk polarization holographic recording material of phenanthrenequinone-doped polymethyl methacrylate photopolymer (PQ-PMMA). The mixed mass ratio of methyl methacrylate (MMA), azobisisobutyronitrile (AIBN) and phenanthrenequinone (PQ) are 100:1:1. Under the cross-angle of π/2 inside the recording media, the polarized holographic reconstruction of the circular polarization recorded by a horizontal linear polarization wave is calculated. It is found that the circularly polarized signal can be faithful reconstruction by arbitrarily polarized reading waves. However, when the polarization of the reading wave is orthogonal to the polarization of the reference wave, it will occur the null reconstruction (NR). The FR technology will provide a simpler and more effective method for a circular polarization generator. At the same time, the NR technology can quickly detect that the polarized wave is vertical polarization.

Research of holographic storage security is of great significance to the development of holographic storage technology. To ensure the difficulty of cracking, the data reconstructed by the wrong key should present a statistically independent random noise distribution as far as possible. This paper studies collinear holographic encryption storage based on the orthogonal Hadamard matrix and random phase. After storing data with a particular key A in a regular ring shape, the secret key A can reconstruct the data. However, some other keys can also reconstruct partial data (crosstalk noise), and this crosstalk greatly reduced the security of the data storage system. Here, random orthogonal phase coding is proposed to solve the crosstalk problem, and the reference light was equally divided into 64 pieces. Each one consists of the same number of pixels at random positions in the circular reference light. The randomness of each reference pixel ensures the consistency of the reconstructed data light intensity, and the data can be completely eliminated due to the orthogonality of the reference light. The orthogonal reconstructed data presents a nearly statistical independent noise distribution, which has effectively reduced the similarity between the original data and the reconstructed data by a wrong key, avoided data leakage, and improved the security of holographic encryption storage.

Exponential growth of data motivates scientists to develop novel optical data storage technologies with the merits of low cost, large capacity, long lifetime, and low power consumption, thus facilitates the development of low-carbon and environmentally friendly economy. Volume holographic data storage, as a promising new generation optical data storage technology, has attracted a tremendous amount of attention within the scientific community, and the lack of appropriate storage medium seriously hinder its large-scale commercial applications. PQ/PMMA photopolymers possess excellent characteristics of low cost, neglectable volume shrinkage and controllable thickness for holographic data storage, while poor holographic performance inhibits its direct applications. Herein, via simply introducing C60 nanoparticles in PQ/PMMA, we successfully synthesize photopolymer with a record-high diffraction efficiency and refractive index modulation, for the first time, reaching up to ~80% and ~1.13×10-4, respectively. More interestingly, C60 nanoparticles here dramatically enhance the intensity holography, but seriously suppress the polarized holographic one. Experimental characterizations and theoretical simulations demonstrate that polarization sensitive holographic performance and reduction of photoinduced anisotropy induced by C60 stem from the strong π-π non-bonding interactions between PQ photosensitizers and C60 molecules (supramolecular) but not chemical reactions. Moreover, C60-PQ/PMMA show a great potential for holographic data storage, exhibiting high chemical stability under extreme working conditions and the angle-multiplexing of 321 gratings and corresponding holographic images are successfully recorded and read on it. Acknowledgment: This work was financially supported by the National Key R&D Program of China (Grant NO. 2018YFA0701800)