2.5D photonic nanostructures with narrow‐band diffraction characteristics have a vast range of potential applications in information storage, tunable lasers, optical filters, and biosensors. However, fabrication of 2.5D photonic devices over large areas remains expertise‐dependent, inaccurate, and high‐cost, limiting their widespread use in practical applications and consumer products. Here, large area printing of quasi 2.5D holograms is demonstrated in the visible spectrum. These holographic surface‐relief gratings are hexagonally packed lateral microscale honeycomb pyramids consisting of vertical nanoscale steps. The consecutive steps act as Bragg gratings producing constructive interference of selective visible wavelengths. The 2.5D nanostepped pyramids exhibit coloration due to the narrow‐band Bragg diffraction that is tuned in the visible spectrum and a wide angular range. Roll‐to‐roll processing allows for rapid nanoimprinting the 2.5D nanostepped pyramid arrays over large areas of acrylate polymer film on poly(ethylene terephthalate) substrate. The utilities of the 2.5D holograms are demonstrated by creating colorimetric refractive index and relative humidity sensors, quick response codes, fingerprints, signatures, and encrypted labels. It is envisioned that 2.5D holograms can be integrated with desktop dot‐matrix printers for application in sensing, data storage, and security.

In recent years, functionalized photopolymer systems capable of holographic recording are in great demand due to their potential use in the development of holographic sensors. This work presents a newly developed N-isopropylacrylamide (NIPA)-based photopolymer for holographic recording in reflection and transmission modes. The optimized composition of the material is found to reach refractive index modulation of up to 5×10 and 1.6×10 after recording in transmission and reflection mode, respectively. In addition to fulfilling the requirements for holographic recording materials, the NIPA-based photopolymer is sensitive to temperature and has lower toxicity than acrylamide-based photopolymers. Possible application of the NIPA-based photopolymer in the development of a holographic temperature sensor is discussed.

The aim of this paper is to discuss the benefits as well as the limitations of utilizing photopolymer materials in the design of holograms that are responsive to changes in their environment, such as changes in the concentration of a specific substance, temperature, and pressure. Three different case studies are presented, including both surface and volume phase holograms, in order to demonstrate the flexibility in the approach of utilizing holographic photopolymers for the design of sensors and interactive optical devices. First, a functionalized surface relief hologram is demonstrated to operate as an optical sensor for the detection of metal ions in water. The sensitivity and selectivity of the sensor are investigated. The second example demonstrates a volume transmission hologram recorded in a temperature-sensitive photopolymer and the memory effects of its exposure to elevated temperature. Finally, a pressure-sensitive reflection hologram that changes color under application of pressure is characterized, and its potential application in document authentication is described.

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This paper explores the effects of humidity on gratings recorded in a polyvinylalcohol–acrylamide photopolymer medium. Investigation of the behaviour of transmission gratings exposed to high humidity is of significant interest for two reasons, firstly because the grating’s sensitivity to humidity can be exploited for the development of irreversible humidity indicators, secondly because too much sensitivity to humidity can limit the use of these materials in applications where an environmentally stable hologram is needed. In this paper we focus on the effect of high humidity on the properties of volume phase transmission gratings recorded in PVA/AA photopolymer layers in the temperature range 8–24 ° C. It has been found that although exposure to humidity changes the diffraction efficiency and Bragg angle of gratings, the effects are fully reversible if the temperatures are kept low. For example, when gratings were subjected to relative humidities of 80% and 90% at a temperature of 8 ° C the observed changes were fully reversible. However, irreversible changes in diffraction efficiency, thickness, refractive index modulation and Bragg angle were observed when the temperature during the humidity exposure was higher than 16 ° C. The magnitude of the irreversible changes depends strongly on the ambient temperature during the humidity exposure, the humidity level and also on the duration of the humidity exposure.